One document matched: draft-ietf-mpls-rfc4379bis-07.xml
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]>
<rfc category="std" docName="draft-ietf-mpls-rfc4379bis-07"
obsoletes="4379, 6424, 6829, 7537"
ipr="pre5378Trust200902">
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<?rfc toc="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes"?>
<?rfc iprnotified="no" ?>
<?rfc strict="yes" ?>
<front>
<title abbrev="Detecting MPLS Data Plane Failures">Detecting
Multi-Protocol Label Switched (MPLS) Data Plane Failures</title>
<author fullname="Kireeti Kompella" initials="K." surname="Kompella">
<organization>Juniper Networks, Inc.</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<country/>
</postal>
<email>kireeti.kompella@gmail.com</email>
</address>
</author>
<author role="editor" fullname="Carlos Pignataro" initials="C." surname="Pignataro">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<country/>
</postal>
<email>cpignata@cisco.com</email>
</address>
</author>
<author fullname="Nagendra Kumar" initials="N." surname="Kumar">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<country/>
</postal>
<email>naikumar@cisco.com</email>
</address>
</author>
<author fullname="Sam Aldrin" initials="S." surname="Aldrin">
<organization>Google</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<country/>
</postal>
<email>aldrin.ietf@gmail.com</email>
</address>
</author>
<author fullname="Mach(Guoyi) Chen" initials="M." surname="Chen">
<organization>Huawei</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<country/>
</postal>
<email>mach.chen@huawei.com</email>
</address>
</author>
<date/>
<abstract>
<t>This document describes a simple and efficient mechanism that can be
used to detect data plane failures in Multi-Protocol Label Switching
(MPLS) Label Switched Paths (LSPs). There are two parts to this
document: information carried in an MPLS "echo request" and "echo reply"
for the purposes of fault detection and isolation, and mechanisms for
reliably sending the echo reply.</t>
<t>This document obsoletes RFCs 4379, 6424, 6829, and 7537.</t>
</abstract>
</front>
<middle>
<section title=" Introduction">
<t>This document describes a simple and efficient mechanism that can be
used to detect data plane failures in MPLS Label Switched Paths (LSPs).
There are two parts to this document: information carried in an MPLS
"echo request" and "echo reply", and mechanisms for transporting the
echo reply. The first part aims at providing enough information to check
correct operation of the data plane, as well as a mechanism to verify
the data plane against the control plane, and thereby localize faults.
The second part suggests two methods of reliable reply channels for the
echo request message for more robust fault isolation.</t>
<t>An important consideration in this design is that MPLS echo requests
follow the same data path that normal MPLS packets would traverse. MPLS
echo requests are meant primarily to validate the data plane, and
secondarily to verify the data plane against the control plane.
Mechanisms to check the control plane are valuable, but are not covered
in this document.</t>
<t>This document makes special use of the address range 127/8. This is
an exception to the behavior defined in RFC 1122 <xref
target="RFC1122"/> and updates that RFC. The motivation for this change
and the details of this exceptional use are discussed in section 2.1
below.</t>
<t>This document obsoletes RFC 4379 <xref target="RFC4379"/>,
RFC 6424 <xref target="RFC6424"/>,
RFC 6829 <xref target="RFC6829"/>,
and RFC 7537 <xref target="RFC7537"/>.</t>
<section title=" Conventions">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 <xref
target="RFC2119"/>.</t>
<t>The term "Must Be Zero" (MBZ) is used in object descriptions for
reserved fields. These fields MUST be set to zero when sent and
ignored on receipt.</t>
<t>Terminology pertaining to L2 and L3 Virtual Private Networks (VPNs)
is defined in <xref target="RFC4026"/>.</t>
<t>Since this document refers to the MPLS Time to Live (TTL) far more
frequently than the IP TTL, the authors have chosen the convention of
using the unqualified "TTL" to mean "MPLS TTL" and using "IP TTL" for
the TTL value in the IP header.</t>
</section>
<section title=" Structure of This Document">
<t>The body of this memo contains four main parts: motivation, MPLS
echo request/reply packet format, LSP ping operation, and a reliable
return path. It is suggested that first-time readers skip the actual
packet formats and read the Theory of Operation first; the document is
structured the way it is to avoid forward references.</t>
</section>
<section title=" Contributors">
<t>A mechanism used to detect data plane failures in Multi-Protocol
Label Switching (MPLS) Label Switched Paths (LSPs) was originally
published as RFC 4379 in February 2006. It was produced by the MPLS
Working Group of the IETF and was jointly authored by Kireeti Kompella
and George Swallow.</t>
<t>The following made vital contributions to all aspects of the
original RFC 4379, and much of the material came out of debate and
discussion among this group. <list>
<?rfc subcompact="yes"?>
<t>Ronald P. Bonica, Juniper Networks, Inc.</t>
<t>Dave Cooper, Global Crossing</t>
<t>Ping Pan, Hammerhead Systems</t>
<t>Nischal Sheth, Juniper Networks, Inc.</t>
<t>Sanjay Wadhwa, Juniper Networks, Inc.</t>
<?rfc subcompact="no"?>
</list></t>
</section>
<section title="Scope of RFC4379bis work">
<t>The primary goal of this document is to provide a clean and updated LSP Ping specification.
</t>
<t><xref target="RFC4379"/> defines the basic mechanism for MPLS LSP
validation that can be used for fault detection and isolation. The
scope of this document also is to address various
updates to MPLS LSP Ping, including:
<list style="symbols">
<t>Update all references and citations.
<list style="symbols">
<t>Obsoleted RFCs 2434, 2030, and 3036 are respectively replaced with RFCs 5226, 5905, and 5036.</t>
<t>Additionally, these three documents published as RFCs: RFCs 4447, 4761, and 5085.</t>
</list>
</t>
<t>Incorporate all outstanding Errata.
<list style="symbols">
<t>Erratum with IDs: 108, 1418, 1714, 1786, 3399, 742, and 2978.</t>
</list></t>
<t>Replace EXP with Traffic Class (TC), based on the update from RFC 5462.</t>
<t>Incorporate the updates from RFC 6829, by adding the PW FECs advertised over IPv6, and obsoleting RFC 6829.</t>
<t>Incorporate the updates from RFC 7506, by adding IPv6 Router Alert Option for MPLS OAM.</t>
<t>
Incorporate newly defined bits on the Global Flags field, from RFC 6425 and RFC 6426.
</t>
<t>Update the IPv4 addresses used in examples to utilize the documentation prefix. Add examples with IPv6 addresses.</t>
<t>Incorporate the updates from RFC 6424, by deprecating the Downstream Mapping TLV (DSMAP) and adding the Downstream Detailed Mapping TLV (DDMAP), updating two new return codes, updating the procedures, IANA section, Security Considerations, and obsoleting RFC 6424.</t>
<t>Incorporate the updates from RFC 7537, by updating the IANA Considerations Section, and obsoleting RFC 7537.</t>
<t>Finally, obsolete RFC 4379.</t>
</list>
</t>
</section>
</section>
<section title=" Motivation">
<t>When an LSP fails to deliver user traffic, the failure cannot always
be detected by the MPLS control plane. There is a need to provide a tool
that would enable users to detect such traffic "black holes" or
misrouting within a reasonable period of time, and a mechanism to
isolate faults.</t>
<t>In this document, we describe a mechanism that accomplishes these
goals. This mechanism is modeled after the ping/traceroute paradigm:
ping (ICMP echo request <xref target="RFC0792"/>) is used for connectivity
checks, and traceroute is used for hop-by-hop fault localization as well
as path tracing. This document specifies a "ping" mode and a
"traceroute" mode for testing MPLS LSPs.</t>
<t>The basic idea is to verify that packets that belong to a particular
Forwarding Equivalence Class (FEC) actually end their MPLS path on a
Label Switching Router (LSR) that is an egress for that FEC. This
document proposes that this test be carried out by sending a packet
(called an "MPLS echo request") along the same data path as other
packets belonging to this FEC. An MPLS echo request also carries
information about the FEC whose MPLS path is being verified. This echo
request is forwarded just like any other packet belonging to that FEC.
In "ping" mode (basic connectivity check), the packet should reach the
end of the path, at which point it is sent to the control plane of the
egress LSR, which then verifies whether it is indeed an egress for the
FEC. In "traceroute" mode (fault isolation), the packet is sent to the
control plane of each transit LSR, which performs various checks that it
is indeed a transit LSR for this path; this LSR also returns further
information that helps check the control plane against the data plane,
i.e., that forwarding matches what the routing protocols determined as
the path.
</t>
<t>An LSP traceroute may cross a tunneled or stitched LSP en route
to the destination. While performing end-to-end LSP validation in such scenarios,
the FEC information included in the packet by Initiator may be different from the one
assigned by transit node in different segment of a stitched LSP or tunnel. Let us
consider a simple case.
</t>
<figure>
<artwork><![CDATA[
A B C D E
o -------- o -------- o --------- o --------- o
\_____/ | \______/ \______/ | \______/
LDP | RSVP RSVP | LDP
| |
\____________________/
LDP
]]></artwork>
</figure>
<t>When an LSP traceroute is initiated from Router A to Router E, the FEC information
included in the packet will be LDP while Router C along the path is a pure RSVP node
and does not run LDP. Consequently, node C will be unable to perform FEC validation. The
MPLS echo request should contain sufficient information to allow any transit node within
stitched or tunneled LSP to perform FEC validations to detect any misrouted echo request.
</t>
<t>One way these tools can be used is to periodically ping an FEC to
ensure connectivity. If the ping fails, one can then initiate a
traceroute to determine where the fault lies. One can also periodically
traceroute FECs to verify that forwarding matches the control plane;
however, this places a greater burden on transit LSRs and thus should be
used with caution.</t>
<section title=" Use of Address Range 127/8">
<t>As described above, LSP ping is intended as a diagnostic tool. It
is intended to enable providers of an MPLS-based service to isolate
network faults. In particular, LSP ping needs to diagnose situations
where the control and data planes are out of sync. It performs this by
routing an MPLS echo request packet based solely on its label stack.
That is, the IP destination address is never used in a forwarding
decision. In fact, the sender of an MPLS echo request packet may not
know, a priori, the address of the router at the end of the LSP.</t>
<t>Providers of MPLS-based services also need the ability to trace all
of the possible paths that an LSP may take. Since most MPLS services
are based on IP unicast forwarding, these paths are subject to
equal-cost multi-path (ECMP) load sharing.</t>
<t>This leads to the following requirements: <list style="numbers">
<t>Although the LSP in question may be broken in unknown ways, the
likelihood of a diagnostic packet being delivered to a user of an
MPLS service MUST be held to an absolute minimum.</t>
<t>If an LSP is broken in such a way that it prematurely
terminates, the diagnostic packet MUST NOT be IP forwarded.</t>
<t>A means of varying the diagnostic packets such that they
exercise all ECMP paths is thus REQUIRED.</t>
</list></t>
<t>Clearly, using general unicast addresses satisfies neither of the
first two requirements. A number of other options for addresses were
considered, including a portion of the private address space (as
determined by the network operator) and the newly designated IPv4 link
local addresses. Use of the private address space was deemed
ineffective since the leading MPLS-based service is an IPv4 Virtual
Private Network (VPN). VPNs often use private addresses.</t>
<t>The IPv4 link local addresses are more attractive in that the scope
over which they can be forwarded is limited. However, if one were to
use an address from this range, it would still be possible for the
first recipient of a diagnostic packet that "escaped" from a broken
LSP to have that address assigned to the interface on which it arrived
and thus could mistakenly receive such a packet. Furthermore, the IPv4
link local address range has only recently been allocated. Many
deployed routers would forward a packet with an address from that
range toward the default route.</t>
<t>The 127/8 range for IPv4 and that same range embedded in as
IPv4-mapped IPv6 addresses for IPv6 was chosen for a number of
reasons.</t>
<t>RFC 1122 allocates the 127/8 as "Internal host loopback address"
and states: "Addresses of this form MUST NOT appear outside a host."
Thus, the default behavior of hosts is to discard such packets. This
helps to ensure that if a diagnostic packet is misdirected to a host,
it will be silently discarded.</t>
<t>RFC 1812 <xref target="RFC1812"/> states: <list>
<t>A router SHOULD NOT forward, except over a loopback interface,
any packet that has a destination address on network 127. A router
MAY have a switch that allows the network manager to disable these
checks. If such a switch is provided, it MUST default to
performing the checks.</t>
</list></t>
<t>This helps to ensure that diagnostic packets are never IP
forwarded.</t>
<t>The 127/8 address range provides 16M addresses allowing wide
flexibility in varying addresses to exercise ECMP paths. Finally, as
an implementation optimization, the 127/8 provides an easy means of
identifying possible LSP packets.</t>
</section>
<section title="Router Alert Option">
<t>This document requires the use of the Router Alert Option (RAO) set
in IP header in order to have the transit node process the MPLS OAM payload.
</t>
<t><xref target="RFC2113" /> defines a generic Option Value 0x0 for IPv4 RAO that
alerts transit router to examine the IPv4 packet.
<xref target="RFC7506" /> defines MPLS OAM Option Value 69 for IPv6 RAO to alert
transit routers to examine the IPv6 packet more closely for MPLS OAM purposes.
</t>
<t>The use of the Router Alert IP Option in this document is as follows:
<list><t>
In case of an IPv4 header, the generic IPv4 RAO value 0x0
<xref target="RFC2113" /> SHOULD be used. In case of an IPv6 header, the IPv6 RAO
value (69) for MPLS OAM <xref target="RFC7506" /> MUST be used.</t></list>
</t>
</section>
</section>
<section title=" Packet Format">
<t>An MPLS echo request is a (possibly labeled) IPv4 or IPv6 UDP packet;
the contents of the UDP packet have the following format:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version Number | Global Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Reply mode | Return Code | Return Subcode|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TimeStamp Sent (seconds) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TimeStamp Sent (seconds fraction) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TimeStamp Received (seconds) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TimeStamp Received (seconds fraction) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLVs ... |
. .
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The Version Number is currently 1. (Note: the version number is to be
incremented whenever a change is made that affects the ability of an
implementation to correctly parse or process an MPLS echo
request/reply. These changes include any syntactic or semantic changes
made to any of the fixed fields, or to any Type-Length-Value (TLV) or
sub-TLV assignment or format that is defined at a certain version
number. The version number may not need to be changed if an optional TLV
or sub-TLV is added.)</t>
<t>The Global Flags field is a bit vector with the following format:</t>
<figure>
<artwork><![CDATA[
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ |R|T|V|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>This document defines three flags, the R, T, and V bits; the rest MUST be set to zero
when sending and ignored on receipt.</t>
<t>The V (Validate FEC Stack) flag is set to 1 if the sender wants the
receiver to perform FEC Stack validation; if V is 0, the choice is left
to the receiver.</t>
<t>
The T (Respond Only If TTL Expired) flag MUST be set only in the echo
request packet by the sender. This flag MUST NOT be set in the echo
reply packet. If this flag is set in an echo reply packet, then it
MUST be ignored. The T flag is defined in <xref target="RFC6425" />.
</t>
<t>
The R (Validate Reverse Path) flag is defined in <xref target="RFC6426" />.
When this flag is set in the echo request,
the Responder SHOULD return reverse-path FEC information, as
described in Section 3.4.2 of <xref target="RFC6426" />.
</t>
<t>The Message Type is one of the following:</t>
<figure>
<artwork><![CDATA[
Value Meaning
----- -------
1 MPLS echo request
2 MPLS echo reply
]]></artwork>
</figure>
<t>The Reply Mode can take one of the following values:</t>
<figure>
<artwork><![CDATA[
Value Meaning
----- -------
1 Do not reply
2 Reply via an IPv4/IPv6 UDP packet
3 Reply via an IPv4/IPv6 UDP packet with Router Alert
4 Reply via application level control channel
]]></artwork>
</figure>
<t>An MPLS echo request with 1 (Do not reply) in the Reply Mode field
may be used for one-way connectivity tests; the receiving router may log
gaps in the Sequence Numbers and/or maintain delay/jitter statistics. An
MPLS echo request would normally have 2 (Reply via an IPv4/IPv6
UDP packet) in the Reply Mode field. If the normal IP return path is
deemed unreliable, one may use 3 (Reply via an IPv4/IPv6 UDP packet with
Router Alert). Note that this requires that all intermediate routers
understand and know how to forward MPLS echo replies. The echo reply
uses the same IP version number as the received echo request, i.e., an
IPv4 encapsulated echo reply is sent in response to an IPv4 encapsulated
echo request.</t>
<t>Some applications support an IP control channel. One such example is
the associated control channel defined in Virtual Circuit Connectivity
Verification (VCCV) <xref target="RFC5085"/>. Any application that supports
an IP control channel between its control entities may set the Reply
Mode to 4 (Reply via application level control channel) to ensure that
replies use that same channel. Further definition of this codepoint is
application specific and thus beyond the scope of this document.</t>
<t>Return Codes and Subcodes are described in the next section.</t>
<t>The Sender's Handle is filled in by the sender, and returned
unchanged by the receiver in the echo reply (if any). There are no
semantics associated with this handle, although a sender may find this
useful for matching up requests with replies.</t>
<t>The Sequence Number is assigned by the sender of the MPLS echo
request and can be (for example) used to detect missed replies.</t>
<t>The TimeStamp Sent is the time-of-day
(according to the sender's clock) in NTP format <xref target="RFC5905"/> when
the MPLS echo request is sent. The TimeStamp Received in an echo reply
is the time-of-day (according to the receiver's clock) in NTP format
that the corresponding echo request was received.</t>
<t>TLVs (Type-Length-Value tuples) have the following format:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
. .
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Types are defined below; Length is the length of the Value field in
octets. The Value field depends on the Type; it is zero padded to align
to a 4-octet boundary. TLVs may be nested within other TLVs, in which
case the nested TLVs are called sub-TLVs. Sub-TLVs have independent
types and MUST also be 4-octet aligned.</t>
<t>Two examples of how TLV and sub-TLV length are computed, and of how sub-TLVs are padded
to be 4-octet aligned as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 (LDP IPv4 FEC) | Length = 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The Length for this TLV is 5. A Target FEC Stack TLV that contains an
LDP IPv4 FEC sub-TLV and a VPN IPv4 prefix sub-TLV has the following
format:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 (FEC TLV) | Length = 32 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-Type = 1 (LDP IPv4 FEC) | Length = 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-Type = 6 (VPN IPv4 prefix)| Length = 13 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>A description of the Types and Values of the top-level TLVs for LSP
ping are given below:</t>
<figure>
<artwork><![CDATA[
Type # Value Field
------ -----------
1 Target FEC Stack
2 Downstream Mapping (Deprecated)
3 Pad
4 Not Assigned
5 Vendor Enterprise Number
6 Not Assigned
7 Interface and Label Stack
8 Not Assigned
9 Errored TLVs
10 Reply TOS Byte
20 Downstream Detailed Mapping
]]></artwork>
</figure>
<t>Types less than 32768 (i.e., with the high-order bit equal to 0) are
mandatory TLVs that MUST either be supported by an implementation or
result in the return code of 2 ("One or more of the TLVs was not
understood") being sent in the echo response.</t>
<t>Types greater than or equal to 32768 (i.e., with the high-order bit
equal to 1) are optional TLVs that SHOULD be ignored if the
implementation does not understand or support them.</t>
<section title=" Return Codes">
<t>The Return Code is set to zero by the sender. The receiver can set
it to one of the values listed below. The notation <RSC> refers
to the Return Subcode. This field is filled in with the stack-depth
for those codes that specify that. For all other codes, the Return
Subcode MUST be set to zero.</t>
<figure>
<artwork><![CDATA[
Value Meaning
----- -------
0 No return code
1 Malformed echo request received
2 One or more of the TLVs was not understood
3 Replying router is an egress for the FEC at stack-
depth <RSC>
4 Replying router has no mapping for the FEC at stack-
depth <RSC>
5 Downstream Mapping Mismatch (See Note 1)
6 Upstream Interface Index Unknown (See Note 1)
7 Reserved
8 Label switched at stack-depth <RSC>
9 Label switched but no MPLS forwarding at stack-depth
<RSC>
10 Mapping for this FEC is not the given label at stack-
depth <RSC>
11 No label entry at stack-depth <RSC>
12 Protocol not associated with interface at FEC stack-
depth <RSC>
13 Premature termination of ping due to label stack
shrinking to a single label
14 See DDM TLV for Return Code and Return Subcode
15 Label switched with FEC change
]]></artwork>
</figure>
<t>Note 1 <list>
<t>The Return Subcode contains the point in the label stack where
processing was terminated. If the RSC is 0, no labels were
processed. Otherwise the packet would have been label switched at
depth RSC.</t>
</list></t>
</section>
<section title=" Target FEC Stack">
<t>A Target FEC Stack is a list of sub-TLVs. The number of elements is
determined by looking at the sub-TLV length fields.</t>
<figure>
<artwork><![CDATA[
Sub-Type Length Value Field
-------- ------ -----------
1 5 LDP IPv4 prefix
2 17 LDP IPv6 prefix
3 20 RSVP IPv4 LSP
4 56 RSVP IPv6 LSP
5 Not Assigned
6 13 VPN IPv4 prefix
7 25 VPN IPv6 prefix
8 14 L2 VPN endpoint
9 10 "FEC 128" Pseudowire - IPv4 (deprecated)
10 14 "FEC 128" Pseudowire - IPv4
11 16+ "FEC 129" Pseudowire - IPv4
12 5 BGP labeled IPv4 prefix
13 17 BGP labeled IPv6 prefix
14 5 Generic IPv4 prefix
15 17 Generic IPv6 prefix
16 4 Nil FEC
24 38 "FEC 128" Pseudowire - IPv6
25 40+ "FEC 129" Pseudowire - IPv6
]]></artwork>
</figure>
<t>Other FEC Types will be defined as needed.</t>
<t>Note that this TLV defines a stack of FECs, the first FEC element
corresponding to the top of the label stack, etc.</t>
<t>An MPLS echo request MUST have a Target FEC Stack that describes
the FEC Stack being tested. For example, if an LSR X has an LDP
mapping <xref target="RFC5036"/> for 192.0.2.1 (say, label 1001), then
to verify that label 1001 does indeed reach an egress LSR that
announced this prefix via LDP, X can send an MPLS echo request with an
FEC Stack TLV with one FEC in it, namely, of type LDP IPv4 prefix,
with prefix 192.0.2.1/32, and send the echo request with a label of
1001.</t>
<t>Say LSR X wanted to verify that a label stack of <1001,
23456> is the right label stack to use to reach a VPN IPv4 prefix
[see <xref target='vpnv4'/>] of 203.0.113.0/24 in VPN foo. Say further that LSR
Y with loopback address 192.0.2.1 announced prefix 203.0.113.0/24 with Route
Distinguisher RD-foo-Y (which may in general be different from the
Route Distinguisher that LSR X uses in its own advertisements for VPN
foo), label 23456 and BGP next hop 192.0.2.1 <xref target="RFC4271"/>.
Finally, suppose that LSR X receives a label binding of 1001 for
192.0.2.1 via LDP. X has two choices in sending an MPLS echo
request: X can send an MPLS echo request with an FEC Stack TLV with a
single FEC of type VPN IPv4 prefix with a prefix of 203.0.113.0/24 and a Route
Distinguisher of RD-foo-Y. Alternatively, X can send an FEC Stack TLV
with two FECs, the first of type LDP IPv4 with a prefix of
192.0.2.1/32 and the second of type of IP VPN with a prefix 203.0.113.0/24
with Route Distinguisher of RD-foo-Y. In either case, the MPLS echo
request would have a label stack of <1001, 23456>. (Note: in
this example, 1001 is the "outer" label and 23456 is the "inner"
label.)</t>
<t>
If, for example, an LSR Y has an LDP mapping for the IPv6 address 2001:db8::1 (say, label 2001),
then to verify that label 2001 does reach an egress LSR that announced this previx via LDP,
LSR Y can send an MPLS echo request with an
FEC Stack TLV with one LDP IPv6 prefix FEC, with prefix 2001:db8::1/128, and with a label of 2001.
</t>
<t>If an end-to-end path comprises of one or more tunneled or stitched LSPs, each transit node
that is the originating point of a new tunnel or segment SHOULD reply back notifying the FEC
stack change along with the new FEC details. For example, if LSR X has an LDP
mapping for IPv4 prefix 192.0.2.10 on LSR Z (say, label 3001). Say further that
LSR A and LSR B are transit nodes along the path which also have an RSVP tunnel over
which LDP is enabled. While replying back, A SHOULD notify that the FEC changes from
LDP to <RSVP, LDP>. If the new tunnel is a transparent
pipe, i.e. the data-plane trace will not expire in the middle of the tunnel, then
the transit node SHOULD NOT reply back notifying the FEC stack change or the new
FEC details. If the transit node wishes to hide the nature of the tunnel from the
ingress of the echo request, then the transit node MAY notify the FEC stack change
and include Nil FEC as the new FEC.
</t>
<section title=" LDP IPv4 Prefix">
<t>The IPv4 Prefix FEC is defined in <xref target="RFC5036"/>. When an
LDP IPv4 prefix is encoded in a label stack, the following format is
used. The value consists of 4 octets of an IPv4 prefix followed by 1
octet of prefix length in bits; the format is given below. The IPv4
prefix is in network byte order; if the prefix is shorter than 32
bits, trailing bits SHOULD be set to zero. See <xref target="RFC5036"/>
for an example of a Mapping for an IPv4 FEC.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" LDP IPv6 Prefix">
<t>The IPv6 Prefix FEC is defined in <xref target="RFC5036"/>. When an
LDP IPv6 prefix is encoded in a label stack, the following format is
used. The value consists of 16 octets of an IPv6 prefix followed by
1 octet of prefix length in bits; the format is given below. The
IPv6 prefix is in network byte order; if the prefix is shorter than
128 bits, the trailing bits SHOULD be set to zero. See <xref
target="RFC5036"/> for an example of a Mapping for an IPv6 FEC.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 prefix |
| (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" RSVP IPv4 LSP">
<t>The value has the format below. The value fields are taken from
RFC 3209, sections 4.6.1.1 and 4.6.2.1. See <xref
target="RFC3209"/>.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel end point address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel sender address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" RSVP IPv6 LSP">
<t>The value has the format below. The value fields are taken from
RFC 3209, sections 4.6.1.2 and 4.6.2.2. See <xref
target="RFC3209"/>.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 tunnel end point address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 tunnel sender address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title="VPN IPv4 Prefix" anchor='vpnv4'>
<t>VPN-IPv4 Network Layer Routing Information (NLRI) is defined in
<xref target="RFC4365"/>. This document uses the term VPN IPv4
prefix for a VPN-IPv4 NLRI that has been advertised with an MPLS
label in BGP. See <xref target="RFC3107"/>.</t>
<t>When a VPN IPv4 prefix is encoded in a label stack, the following
format is used. The value field consists of the Route Distinguisher
advertised with the VPN IPv4 prefix, the IPv4 prefix (with trailing
0 bits to make 32 bits in all), and a prefix length, as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The Route Distinguisher (RD) is an 8-octet identifier; it does
not contain any inherent information. The purpose of the RD is
solely to allow one to create distinct routes to a common IPv4
address prefix. The encoding of the RD is not important here. When
matching this field to the local FEC information, it is treated as
an opaque value.</t>
</section>
<section title=" VPN IPv6 Prefix">
<t>VPN-IPv6 Network Layer Routing Information (NLRI) is defined in
<xref target="RFC4365"/>. This document uses the term VPN IPv6
prefix for a VPN-IPv6 NLRI that has been advertised with an MPLS
label in BGP. See <xref target="RFC3107"/>.</t>
<t>When a VPN IPv6 prefix is encoded in a label stack, the following
format is used. The value field consists of the Route Distinguisher
advertised with the VPN IPv6 prefix, the IPv6 prefix (with trailing
0 bits to make 128 bits in all), and a prefix length, as
follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 prefix |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The Route Distinguisher is identical to the VPN IPv4 Prefix RD,
except that it functions here to allow the creation of distinct
routes to IPv6 prefixes. See <xref target='vpnv4'/>. When matching
this field to local FEC information, it is treated as an opaque value.
</t>
</section>
<section title=" L2 VPN Endpoint">
<t>VPLS stands for Virtual Private LAN Service. The terms VPLS BGP
NLRI and VE ID (VPLS Edge Identifier) are defined in <xref
target="RFC4761"/>. This document uses the simpler term L2 VPN
endpoint when referring to a VPLS BGP NLRI. The Route Distinguisher
is an 8-octet identifier used to distinguish information about
various L2 VPNs advertised by a node. The VE ID is a 2-octet
identifier used to identify a particular node that serves as the
service attachment point within a VPLS. The structure of these two
identifiers is unimportant here; when matching these fields to local
FEC information, they are treated as opaque values. The
encapsulation type is identical to the PW Type in section 3.2.8
below.</t>
<t>When an L2 VPN endpoint is encoded in a label stack, the
following format is used. The value field consists of a Route
Distinguisher (8 octets), the sender (of the ping)'s VE ID (2
octets), the receiver's VE ID (2 octets), and an encapsulation type
(2 octets), formatted as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's VE ID | Receiver's VE ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encapsulation Type | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" FEC 128 Pseudowire - IPv4 (Deprecated)">
<t>See <xref target='fec128-old'/> for details
</t>
</section>
<section title=" FEC 128 Pseudowire - IPv4 (Current)">
<t>FEC 128 (0x80) is defined in <xref target="RFC4447"/>, as are
the terms PW ID (Pseudowire ID) and PW Type (Pseudowire Type). A PW
ID is a non-zero 32-bit connection ID. The PW Type is a 15-bit
number indicating the encapsulation type. It is carried right
justified in the field below termed encapsulation type with the
high-order bit set to zero.</t>
<t>Both of these fields are treated in this protocol as opaque
values. When matching these field to the local FEC information, the
match MUST be exact.</t>
<t>When an FEC 128 is encoded in a label stack, the following format
is used. The value field consists of the sender's PE IPv4 address (the
source address of the targeted LDP session), the remote PE IPv4 address
(the destination address of the targeted LDP session), the PW ID,
and the encapsulation type as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Type | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" FEC 129 Pseudowire - IPv4">
<t>FEC 129 (0x81) and the terms PW Type, Attachment Group Identifier
(AGI), Attachment Group Identifier Type (AGI Type), Attachment
Individual Identifier Type (AII Type), Source Attachment Individual
Identifier (SAII), and Target Attachment Individual Identifier
(TAII) are defined in <xref target="RFC4447"/>. The PW Type is a
15-bit number indicating the encapsulation type. It is carried right
justified in the field below PW Type with the high-order bit set to
zero. All the other fields are treated as opaque values and copied
directly from the FEC 129 format. All of these values together
uniquely define the FEC within the scope of the LDP session
identified by the source and remote PE IPv4 addresses.</t>
<t>When an FEC 129 is encoded in a label stack, the following format
is used. The Length of this TLV is 16 + AGI length + SAII length +
TAII length. Padding is used to make the total length a multiple of
4; the length of the padding is not included in the Length
field.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Type | AGI Type | AGI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | SAII Length | SAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (continued) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | TAII Length | TAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (continued) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TAII (cont.) | 0-3 octets of zero padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title="FEC 128 Pseudowire - IPv6">
<t>The FEC 128 Pseudowire IPv6 sub-TLV has a structure consistent with
the FEC 128 Pseudowire IPv4 sub-TLV as described in Section 3.2.9.
The value field consists of the Sender's PE IPv6 address (the
source address of the targeted LDP session), the remote PE IPv6 address (the
destination address of the targeted LDP session), the PW ID, and the
encapsulation type as follows:
</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Sender's PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Remote PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Type | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Sender's PE IPv6 Address: The source IP address of the target IPv6 LDP
session. 16 octets.
</t>
<t>Remote PE IPv6 Address: The destination IP address of the target IPv6
LDP session. 16 octets.
</t>
<t>PW ID: Same as FEC 128 Pseudowire IPv4 in Section 3.2.9.
</t>
<t>PW Type: Same as FEC 128 Pseudowire IPv4 in Section 3.2.9.
</t>
</section>
<section title="FEC 129 Pseudowire - IPv6">
<t>The FEC 129 Pseudowire IPv6 sub-TLV has a structure consistent with
the FEC 129 Pseudowire IPv4 sub-TLV as described in Section 3.2.10.
When an FEC 129 is encoded in a label stack, the following format is
used. The length of this TLV is 40 + AGI (Attachment Group Identifier)
length + SAII (Source Attachment Individual Identifier) length + TAII
(Target Attachment Individual Identifier) length. Padding is used to
make the total length a multiple of 4; the length of the padding is
not included in the Length field.
</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Sender's PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Remote PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Type | AGI Type | AGI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | SAII Length | SAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (continued) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | TAII Length | TAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (continued) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TAII (cont.) | 0-3 octets of zero padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Sender's PE IPv6 Address: The source IP address of the target IPv6
LDP session. 16 octets.
</t>
<t>Remote PE IPv6 Address: The destination IP address of the target IPv6
LDP session. 16 octets.
</t>
<t>The other fields are the same as FEC 129 Pseudowire IPv4 in Section 3.2.10.
</t>
</section>
<section title=" BGP Labeled IPv4 Prefix">
<t>BGP labeled IPv4 prefixes are defined in <xref
target="RFC3107"/>. When a BGP labeled IPv4 prefix is encoded in a
label stack, the following format is used. The value field consists
the IPv4 prefix (with trailing 0 bits to make 32 bits in all), and
the prefix length, as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" BGP Labeled IPv6 Prefix">
<t>BGP labeled IPv6 prefixes are defined in <xref
target="RFC3107"/>. When a BGP labeled IPv6 prefix is encoded in a
label stack, the following format is used. The value consists of 16
octets of an IPv6 prefix followed by 1 octet of prefix length in
bits; the format is given below. The IPv6 prefix is in network byte
order; if the prefix is shorter than 128 bits, the trailing bits
SHOULD be set to zero.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 prefix |
| (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" Generic IPv4 Prefix">
<t>The value consists of 4 octets of an IPv4 prefix followed by 1
octet of prefix length in bits; the format is given below. The IPv4
prefix is in network byte order; if the prefix is shorter than 32
bits, trailing bits SHOULD be set to zero. This FEC is used if the
protocol advertising the label is unknown or may change during the
course of the LSP. An example is an inter-AS LSP that may be
signaled by LDP in one Autonomous System (AS), by RSVP-TE <xref
target="RFC3209"/> in another AS, and by BGP between the ASes, such
as is common for inter-AS VPNs.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" Generic IPv6 Prefix">
<t>The value consists of 16 octets of an IPv6 prefix followed by 1
octet of prefix length in bits; the format is given below. The IPv6
prefix is in network byte order; if the prefix is shorter than 128
bits, the trailing bits SHOULD be set to zero.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 prefix |
| (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" Nil FEC">
<t>At times, labels from the reserved range, e.g., Router Alert and
Explicit-null, may be added to the label stack for various
diagnostic purposes such as influencing load-balancing. These labels
may have no explicit FEC associated with them. The Nil FEC Stack is
defined to allow a Target FEC Stack sub-TLV to be added to the
Target FEC Stack to account for such labels so that proper
validation can still be performed.</t>
<t>The Length is 4. Labels are 20-bit values treated as numbers.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Label is the actual label value inserted in the label stack; the
MBZ fields MUST be zero when sent and ignored on receipt.</t>
</section>
</section>
<section title= "Downstream Mapping (Deprecated)">
<t>See <xref target='dm-old'/> for more details.
</t>
</section>
<section title=" Downstream Detailed Mapping TLV" anchor='ddm'>
<t>The Downstream Detailed Mapping object is a TLV that MAY be included
in an MPLS echo request message. Only one Downstream Detailed
Mapping object may appear in an echo request. The presence of a
Downstream Detailed Mapping object is a request that Downstream
Detailed Mapping objects be included in the MPLS echo reply. If the
replying router is the destination (Label Edge Router) of the FEC,
then a Downstream Detailed Mapping TLV SHOULD NOT be included in the
MPLS echo reply. Otherwise, the replying router SHOULD include a
Downstream Detailed Mapping object for each interface over which this
FEC could be forwarded.
</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU | Address Type | DS Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Interface Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Code | Return Subcode| Sub-tlv Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. List of Sub-TLVs .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The Downstream Detailed Mapping TLV format is derived from the
Downstream Mapping TLV format (Appendix A.2). The key change is that
variable length and optional fields have been converted into sub-TLVs. The
fields have the same use and meaning as defined in Appendix A.2. A
summary of the fields taken from the Downstream Mapping TLV is as below:
</t>
<t>Maximum Transmission Unit (MTU)
<list>
<t>The MTU is the size in octets of the largest MPLS frame (including
label stack) that fits on the interface to the Downstream Label
Switching Router (LSR).
</t>
</list>
</t>
<t>Address Type
<list>
<t>The Address Type indicates if the interface is numbered or
unnumbered. It also determines the length of the Downstream IP
Address and Downstream Interface fields.
</t>
</list>
</t>
<t>DS Flags
<list>
<t>The DS Flags field is a bit vector of various flags.
</t>
</list>
</t>
<t>Downstream Address and Downstream Interface Address
<list>
<t>IPv4 addresses and interface indices are encoded in 4 octets; IPv6
addresses are encoded in 16 octets. For details regarding setting
the address value, refer to Appendix A.2.
</t>
</list>
</t>
<t>Return Code
<list>
<t>The Return Code is set to zero by the sender. The receiver can
set it to one of the values specified in the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
registry, "Return Codes" sub-registry.
</t>
<t>If the receiver sets a non-zero value of the Return Code field in
the Downstream Detailed Mapping TLV, then the receiver MUST also
set the Return Code field in the echo reply header to "See DDM TLV
for Return Code and Return Subcode" (Section 3.1). An exception
to this is if the receiver is a bud node <xref target="RFC4461" /> and is replying
as both an egress and a transit node with a Return Code of 3
("Replying router is an egress for the FEC at stack-depth <RSC>")
in the echo reply header.
</t>
<t>If the Return Code of the echo reply message is not set to either
"See DDM TLV for Return Code and Return Subcode" (Section 3.1) or
"Replying router is an egress for the FEC at stack-depth <RSC>",
then the Return Code specified in the Downstream Detailed Mapping
TLV MUST be ignored.
</t>
</list>
</t>
<t>Return Subcode
<list>
<t>The Return Subcode is set to zero by the sender. The receiver can
set it to one of the values specified in the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
registry, "Return Codes" sub-registry. This field is filled in
with the stack-depth for those codes that specify the stack-depth.
For all other codes, the Return Subcode MUST be set to zero.
</t>
<t>If the Return Code of the echo reply message is not set to either
"See DDM TLV for Return Code and Return Subcode" (Section 3.1) or
"Replying router is an egress for the FEC at stack-depth <RSC>",
then the Return Subcode specified in the Downstream Detailed
Mapping TLV MUST be ignored.
</t>
</list>
</t>
<t>Sub-tlv Length
<list>
<t>Total length in bytes of the sub-TLVs associated with this TLV.
</t>
</list>
</t>
<section title="Sub-TLVs">
<t>This section defines the sub-TLVs that MAY be included as part of the
Downstream Detailed Mapping TLV.
</t>
<figure>
<artwork><![CDATA[
Sub-Type Value Field
--------- ------------
1 Multipath data
2 Label stack
3 FEC stack change
]]></artwork>
</figure>
<section title="Multipath Data Sub-TLV">
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Multipath Type | Multipath Length |Reserved (MBZ) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| (Multipath Information) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The multipath data sub-TLV includes Multipath Information. The sub-
TLV fields and their usage is as defined in Appendix A.2. A brief
summary of the fields is as below:
</t>
<t>Multipath Type
<list>
<t>The type of the encoding for the Multipath Information.
</t>
</list>
</t>
<t>Multipath Length
<list>
<t>The length in octets of the Multipath Information.
</t>
</list>
</t>
<t>MBZ
<list>
<t>MUST be set to zero when sending; MUST be ignored on receipt.
</t>
</list>
</t>
<t>Multipath Information
<list>
<t>Encoded multipath data, according to the Multipath Type.
</t>
</list>
</t>
</section>
<section anchor="S3312-6424" title="Label Stack Sub-TLV">
<t>
</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The Label stack sub-TLV contains the set of labels in the label stack
as it would have appeared if this router were forwarding the packet
through this interface. Any Implicit Null labels are explicitly
included. The number of label/protocol pairs present in the sub-TLV
is determined based on the sub-TLV data length. The label format and
protocol type are as defined in Appendix A.2. When the Downstream
Detailed Mapping TLV is sent in the echo reply, this sub-TLV MUST be
included.
</t>
<t>Downstream Label
<list>
<t>A Downstream label is 24 bits, in the same format as an MPLS label
minus the Time to Live (TTL) field, i.e., the MSBit of the label
is bit 0, the LSBit is bit 19, the Traffic Class (TC) field
<xref target="RFC5462" /> is bits 20-22, and S is bit 23. The replying router
SHOULD fill in the TC field and S bit; the LSR receiving the echo
reply MAY choose to ignore these.
</t>
</list>
</t>
<t>Protocol
<list>
<t>This specifies the label distribution protocol for the Downstream
label.
</t>
</list>
</t>
</section>
<section anchor="S3313-6424" title="FEC Stack Change Sub-TLV">
<t>A router MUST include the FEC stack change sub-TLV when the
downstream node in the echo reply has a different FEC Stack than the
FEC Stack received in the echo request. One or more FEC stack change
sub-TLVs MAY be present in the Downstream Detailed Mapping TLV. The
format is as below.
</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Operation Type | Address Type | FEC-tlv length| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Peer Address (0, 4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. FEC TLV .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Operation Type
<list>
<t>The operation type specifies the action associated with the FEC
stack change. The following operation types are defined:
</t>
</list>
</t>
<figure>
<artwork><![CDATA[
Type # Operation
------ ---------
1 Push
2 Pop
]]></artwork>
</figure>
<t>Address Type
<list>
<t>The Address Type indicates the remote peer's address type. The
Address Type is set to one of the following values. The length of
the peer address is determined based on the address type. The
address type MAY be different from the address type included in
the Downstream Detailed Mapping TLV. This can happen when the LSP
goes over a tunnel of a different address family. The address
type MAY be set to Unspecified if the peer address is either
unavailable or the transit router does not wish to provide it for
security or administrative reasons.
</t>
</list>
</t>
<figure>
<artwork><![CDATA[
Type # Address Type Address length
------ ------------ --------------
0 Unspecified 0
1 IPv4 4
2 IPv6 16
]]></artwork>
</figure>
<t>FEC TLV Length
<list>
<t>Length in bytes of the FEC TLV.
</t>
</list>
</t>
<t>Reserved
<list>
<t>This field is reserved for future use and MUST be set to zero.
</t>
</list>
</t>
<t>Remote Peer Address
<list>
<t>The remote peer address specifies the remote peer that is the
next-hop for the FEC being currently traced.
If the operation type is PUSH, the remote
peer address is the address of the peer from which the FEC being
pushed was learned. If the operation type is POP, the remote peer
address MAY be set to Unspecified.
</t>
<t>For upstream-assigned labels <xref target="RFC5331" />, an operation type of POP
will have a remote peer address (the upstream node that assigned
the label) and this SHOULD be included in the FEC stack change
sub-TLV. The remote peer address MAY be set to Unspecified if the
address needs to be hidden.
</t>
</list>
</t>
<t>FEC TLV
<list>
<t>The FEC TLV is present only when the FEC-tlv length field is non-
zero. The FEC TLV specifies the FEC associated with the FEC stack
change operation. This TLV MAY be included when the operation
type is POP. It MUST be included when the operation type is PUSH.
The FEC TLV contains exactly one FEC from the list of FECs
specified in Section 3.2. A Nil FEC MAY be associated with a PUSH
operation if the responding router wishes to hide the details of
the FEC being pushed.
</t>
</list>
</t>
<t>FEC stack change sub-TLV operation rules are as follows:
<list style="letters">
<t>A FEC stack change sub-TLV containing a PUSH operation MUST NOT
be followed by a FEC stack change sub-TLV containing a POP
operation.</t>
<t>One or more POP operations MAY be followed by one or more PUSH
operations.
</t>
<t>One FEC stack change sub-TLV MUST be included per FEC stack
change. For example, if 2 labels are going to be pushed, then
one FEC stack change sub-TLV MUST be included for each FEC.
</t>
<t>A FEC splice operation (an operation where one FEC ends and
another FEC starts, MUST be performed by including
a POP type FEC stack change sub-TLV followed by a PUSH type FEC
stack change sub-TLV.
</t>
<t>A Downstream detailed mapping TLV containing only one FEC stack
change sub-TLV with Pop operation is equivalent to IS_EGRESS
(Return Code 3, Section 3.1) for the outermost FEC in the FEC
stack. The ingress router performing the MPLS traceroute MUST
treat such a case as an IS_EGRESS for the outermost FEC.
</t>
</list>
</t>
</section>
</section>
</section>
<section title=" Pad TLV">
<t>The value part of the Pad TLV contains a variable number (>= 1)
of octets. The first octet takes values from the following table; all
the other octets (if any) are ignored. The receiver SHOULD verify that
the TLV is received in its entirety, but otherwise ignores the
contents of this TLV, apart from the first octet.</t>
<figure>
<artwork><![CDATA[
Value Meaning
----- -------
0 Reserved
1 Drop Pad TLV from reply
2 Copy Pad TLV to reply
3-250 Unassigned
251-254 Experimental Use
255 Reserved
]]></artwork>
</figure>
</section>
<section title=" Vendor Enterprise Number">
<t>SMI Private Enterprise Numbers are maintained by IANA. The Length
is always 4; the value is the SMI Private Enterprise code, in network
octet order, of the vendor with a Vendor Private extension to any of
the fields in the fixed part of the message, in which case this TLV
MUST be present. If none of the fields in the fixed part of the
message have Vendor Private extensions, inclusion of this TLV is
OPTIONAL. Vendor Private ranges for Message Types, Reply Modes, and
Return Codes have been defined. When any of these are used, the Vendor
Enterprise Number TLV MUST be included in the message.</t>
</section>
<section title=" Interface and Label Stack">
<t>The Interface and Label Stack TLV MAY be included in a reply
message to report the interface on which the request message was
received and the label stack that was on the packet when it was
received. Only one such object may appear. The purpose of the object
is to allow the upstream router to obtain the exact interface and
label stack information as it appears at the replying LSR.</t>
<t>The Length is K + 4*N octets; N is the number of labels in the
label stack. Values for K are found in the description of Address Type
below. The Value field of this TLV has the following
format:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. Label Stack .
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Address Type <list>
<t>The Address Type indicates if the interface is numbered or
unnumbered. It also determines the length of the IP Address and
Interface fields. The resulting total for the initial part of the
TLV is listed in the table below as "K Octets". The Address Type
is set to one of the following values:</t>
</list></t>
<figure>
<artwork><![CDATA[
Type # Address Type K Octets
------ ------------ --------
0 Reserved 4
1 IPv4 Numbered 12
2 IPv4 Unnumbered 12
3 IPv6 Numbered 36
4 IPv6 Unnumbered 24
5-250 Unassigned
251-254 Experimental Use
255 Reserved
]]></artwork>
</figure>
<t>IP Address and Interface <list>
<t>IPv4 addresses and interface indices are encoded in 4 octets;
IPv6 addresses are encoded in 16 octets.</t>
<t>If the interface upon which the echo request message was
received is numbered, then the Address Type MUST be set to IPv4 or
IPv6, the IP Address MUST be set to either the LSR's Router ID or
the interface address, and the Interface MUST be set to the
interface address.</t>
<t>If the interface is unnumbered, the Address Type MUST be either
IPv4 Unnumbered or IPv6 Unnumbered, the IP Address MUST be the
LSR's Router ID, and the Interface MUST be set to the index
assigned to the interface.</t>
</list></t>
<t>Label Stack <list>
<t>The label stack of the received echo request message. If any
TTL values have been changed by this router, they SHOULD be
restored.</t>
</list></t>
</section>
<section title=" Errored TLVs">
<t>The following TLV is a TLV that MAY be included in an echo reply to
inform the sender of an echo request of mandatory TLVs either not
supported by an implementation or parsed and found to be in error.</t>
<t>The Value field contains the TLVs that were not understood, encoded
as sub-TLVs.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 9 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
. .
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
<section title=" Reply TOS Byte TLV">
<t>This TLV MAY be used by the originator of the echo request to
request that an echo reply be sent with the IP header TOS byte set to
the value specified in the TLV. This TLV has a length of 4 with the
following value field.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply-TOS Byte| Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</section>
</section>
<section title=" Theory of Operation">
<t>An MPLS echo request is used to test a particular LSP. The LSP to be
tested is identified by the "FEC Stack"; for example, if the LSP was set
up via LDP, and is to an egress IP address of 198.51.100.1, the FEC Stack
contains a single element, namely, an LDP IPv4 prefix sub-TLV with value
198.51.100.1/32. If the LSP being tested is an RSVP LSP, the FEC Stack
consists of a single element that captures the RSVP Session and Sender
Template that uniquely identifies the LSP.</t>
<t>FEC Stacks can be more complex. For example, one may wish to test a
VPN IPv4 prefix of 203.0.113.0/24 that is tunneled over an LDP LSP with egress
192.0.2.1. The FEC Stack would then contain two sub-TLVs, the bottom
being a VPN IPv4 prefix, and the top being an LDP IPv4 prefix. If the
underlying (LDP) tunnel were not known, or was considered irrelevant,
the FEC Stack could be a single element with just the VPN IPv4
sub-TLV.</t>
<t>When an MPLS echo request is received, the receiver is expected to
verify that the control plane and data plane are both healthy (for the
FEC Stack being pinged) and that the two planes are in sync. The
procedures for this are in section 4.4 below.</t>
<section title=" Dealing with Equal-Cost Multi-Path (ECMP)">
<t>LSPs need not be simple point-to-point tunnels. Frequently, a
single LSP may originate at several ingresses, and terminate at
several egresses; this is very common with LDP LSPs. LSPs for a given
FEC may also have multiple "next hops" at transit LSRs. At an ingress,
there may also be several different LSPs to choose from to get to the
desired endpoint. Finally, LSPs may have backup paths, detour paths,
and other alternative paths to take should the primary LSP go
down.</t>
<t>To deal with the last two first: it is assumed that the LSR
sourcing MPLS echo requests can force the echo request into any
desired LSP, so choosing among multiple LSPs at the ingress is not an
issue. The problem of probing the various flavors of backup paths that
will typically not be used for forwarding data unless the primary LSP
is down will not be addressed here.</t>
<t>Since the actual LSP and path that a given packet may take may not
be known a priori, it is useful if MPLS echo requests can exercise all
possible paths. This, although desirable, may not be practical,
because the algorithms that a given LSR uses to distribute packets
over alternative paths may be proprietary.</t>
<t>To achieve some degree of coverage of alternate paths, there is a
certain latitude in choosing the destination IP address and source UDP
port for an MPLS echo request. This is clearly not sufficient; in the
case of traceroute, more latitude is offered by means of the Multipath
Information of the Downstream Detailed Mapping TLV. This is used as follows. An
ingress LSR periodically sends an MPLS traceroute message to determine
whether there are multipaths for a given LSP. If so, each hop will
provide some information how each of its downstream paths can be
exercised. The ingress can then send MPLS echo requests that exercise
these paths. If several transit LSRs have ECMP, the ingress may
attempt to compose these to exercise all possible paths. However, full
coverage may not be possible.</t>
</section>
<section title=" Testing LSPs That Are Used to Carry MPLS Payloads">
<t>To detect certain LSP breakages, it may be necessary to encapsulate
an MPLS echo request packet with at least one additional label when
testing LSPs that are used to carry MPLS payloads (such as LSPs used
to carry L2VPN and L3VPN traffic. For example, when testing LDP or
RSVP-TE LSPs, just sending an MPLS echo request packet may not detect
instances where the router immediately upstream of the destination of
the LSP ping may forward the MPLS echo request successfully over an
interface not configured to carry MPLS payloads because of the use of
penultimate hop popping. Since the receiving router has no means to
differentiate whether the IP packet was sent unlabeled or implicitly
labeled, the addition of labels shimmed above the MPLS echo request
(using the Nil FEC) will prevent a router from forwarding such a
packet out unlabeled interfaces.</t>
</section>
<section title=" Sending an MPLS Echo Request">
<t>An MPLS echo request is a UDP packet. The IP header is set as
follows: the source IP address is a routable address of the sender;
the destination IP address is a (randomly chosen) IPv4 address from
the range 127/8 or IPv6 address from the range 0:0:0:0:0:FFFF:7F00:0/104.
The IP TTL is set to 1. The source UDP port is chosen by the sender;
the destination UDP port is set to 3503 (assigned by IANA for MPLS
echo requests). The Router Alert IP option of value 0x0
<xref target="RFC2113" /> for IPv4 or value 69 <xref target="RFC7506" />
for IPv6 MUST be set in IP header. </t>
<t>An MPLS echo request is sent with a label stack corresponding to
the FEC Stack being tested. Note that further labels could be applied
if, for example, the normal route to the topmost FEC in the stack is
via a Traffic Engineered Tunnel <xref target="RFC3209"/>. If all of
the FECs in the stack correspond to Implicit Null labels, the MPLS
echo request is considered unlabeled even if further labels will be
applied in sending the packet.</t>
<t>If the echo request is labeled, one MAY (depending on what is being
pinged) set the TTL of the innermost label to 1, to prevent the ping
request going farther than it should. Examples of where this SHOULD be
done include pinging a VPN IPv4 or IPv6 prefix, an L2 VPN endpoint or
a pseudowire. Preventing the ping request from going too far can also
be accomplished by inserting a Router Alert label above this label;
however, this may lead to the undesired side effect that MPLS echo
requests take a different data path than actual data. For more
information on how these mechanisms can be used for pseudowire
connectivity verification, see <xref target="RFC5085"/>.</t>
<t>In "ping" mode (end-to-end connectivity check), the TTL in the
outermost label is set to 255. In "traceroute" mode (fault isolation
mode), the TTL is set successively to 1, 2, and so on.</t>
<t>The sender chooses a Sender's Handle and a Sequence Number. When
sending subsequent MPLS echo requests, the sender SHOULD increment the
Sequence Number by 1. However, a sender MAY choose to send a group of
echo requests with the same Sequence Number to improve the chance of
arrival of at least one packet with that Sequence Number.</t>
<t>The TimeStamp Sent is set to the time-of-day in NTP format
that the echo request is sent. The TimeStamp Received is
set to zero.</t>
<t>An MPLS echo request MUST have an FEC Stack TLV. Also, the Reply
Mode must be set to the desired reply mode; the Return Code and
Subcode are set to zero. In the "traceroute" mode, the echo request
SHOULD include a Downstream Detailed Mapping TLV.</t>
</section>
<section title=" Receiving an MPLS Echo Request">
<t>Sending an MPLS echo request to the control plane is triggered by
one of the following packet processing exceptions: Router Alert
option, IP TTL expiration, MPLS TTL expiration, MPLS Router Alert
label, or the destination address in the 127/8 address range. The
control plane further identifies it by UDP destination port 3503.</t>
<t>For reporting purposes the bottom of stack is considered to be
stack-depth of 1. This is to establish an absolute reference for the
case where the actual stack may have more labels than there are FECs
in the Target FEC Stack.</t>
<t>Furthermore, in all the error codes listed in this document, a
stack-depth of 0 means "no value specified". This allows compatibility
with existing implementations that do not use the Return Subcode
field.</t>
<t>An LSR X that receives an MPLS echo request then processes it as
follows. <list counter="my_count" style="format %d.">
<t>General packet sanity is verified. If the packet is not
well-formed, LSR X SHOULD send an MPLS Echo Reply with the Return
Code set to "Malformed echo request received" and the Subcode to
zero. If there are any TLVs not marked as "Ignore" that LSR X does
not understand, LSR X SHOULD send an MPLS "TLV not understood" (as
appropriate), and the Subcode set to zero. In the latter case, the
misunderstood TLVs (only) are included as sub-TLVs in an Errored
TLVs TLV in the reply. The header fields Sender's Handle, Sequence
Number, and Timestamp Sent are not examined, but are included in
the MPLS echo reply message.</t>
</list></t>
<t>The algorithm uses the following variables and identifiers: <list
hangIndent="20" style="hanging">
<t hangText="Interface-I:">the interface on which the MPLS echo
request was received.</t>
<t hangText="Stack-R:">the label stack on the packet as it was
received.</t>
<t hangText="Stack-D:">the label stack carried in the "Label Stack sub-TLV" in
Downstream Detailed Mapping TLV (not always present)</t>
<t hangText="Label-L:">the label from the actual stack currently
being examined. Requires no initialization.</t>
<t hangText="Label-stack-depth:">the depth of label being
verified. Initialized to the number of labels in the received
label stack S.</t>
<t hangText="FEC-stack-depth:">depth of the FEC in the Target FEC
Stack that should be used to verify the current actual label.
Requires no initialization.</t>
<t hangText="Best-return-code:">contains the return code for the
echo reply packet as currently best known. As the algorithm
progresses, this code may change depending on the results of
further checks that it performs.</t>
<t hangText="Best-rtn-subcode:">similar to Best-return-code, but
for the Echo Reply Subcode.</t>
<t hangText="FEC-status:">result value returned by the FEC
Checking algorithm described in section 4.4.1.</t>
</list></t>
<t>/* Save receive context information */</t>
<t><list counter="my_count" style="format %d.">
<t>If the echo request is good, LSR X stores the interface over
which the echo was received in Interface-I, and the label stack
with which it came in Stack-R.</t>
</list></t>
<t>/* The rest of the algorithm iterates over the labels in Stack-R,
verifies validity of label values, reports associated label switching
operations (for traceroute), verifies correspondence between the
Stack-R and the Target FEC Stack description in the body of the echo
request, and reports any errors. */</t>
<t>/* The algorithm iterates as follows. */</t>
<t><list counter="my_count" style="format %d.">
<t>Label Validation:</t>
</list></t>
<t><list>
<t>If Label-stack-depth is 0 {</t>
<t>/* The LSR needs to report its being a tail-end for the LSP */
<list>
<t>Set FEC-stack-depth to 1, set Label-L to 3 (Implicit Null).
Set Best-return-code to 3 ("Replying router is an egress for
the FEC at stack depth"), set Best-rtn-subcode to the value of
FEC-stack-depth (1) and go to step 5 (Egress Processing).</t>
</list></t>
<t>}</t>
<t>/* This step assumes there is always an entry for well-known
label values */</t>
<t>Set Label-L to the value extracted from Stack-R at depth
Label-stack-depth. Look up Label-L in the Incoming Label Map (ILM)
to determine if the label has been allocated and an operation is
associated with it.</t>
<t>If there is no entry for L {</t>
<t>/* Indicates a temporary or permanent label synchronization
problem the LSR needs to report an error */ <list>
<t>Set Best-return-code to 11 ("No label entry at
stack-depth") and Best-rtn-subcode to Label-stack-depth. Go to
step 7 (Send Reply Packet).</t>
</list></t>
<t>}</t>
<t>Else { <list>
<t>Retrieve the associated label operation from the
corresponding NHLFE and proceed to step 4 (Label Operation
check).</t>
</list></t>
<t>}</t>
</list></t>
<t><list counter="my_count" style="format %d.">
<t>Label Operation Check</t>
</list></t>
<t><list>
<t>If the label operation is "Pop and Continue Processing" {</t>
<t>/* Includes Explicit Null and Router Alert label cases */ <list>
<t>Iterate to the next label by decrementing Label-stack-depth
and loop back to step 3 (Label Validation).</t>
</list></t>
<t>}</t>
<t>If the label operation is "Swap or Pop and Switch based on
Popped Label" { <list>
<t>Set Best-return-code to 8 ("Label switched at stack-depth")
and Best-rtn-subcode to Label-stack-depth to report transit
switching.</t>
<t>If a Downstream Detailed Mapping TLV is present in the received echo
request { <list>
<t>If the IP address in the TLV is 127.0.0.1 or 0::1 {
<list>
<t>Set Best-return-code to 6 ("Upstream Interface
Index Unknown"). An Interface and Label Stack TLV
SHOULD be included in the reply and filled with
Interface-I and Stack-R.</t>
</list></t>
<t>}</t>
<t>Else { <list>
<t>Verify that the IP address, interface address, and
label stack in the Downstream Detailed Mapping TLV match
Interface-I and Stack-R. If there is a mismatch, set
Best-return-code to 5, "Downstream Mapping Mismatch".
An Interface and Label Stack TLV SHOULD be included in
the reply and filled in based on Interface-I and
Stack-R. Go to step 7 (Send Reply Packet).</t>
</list></t>
<t>}</t>
</list></t>
<t>}</t>
<t>For each available downstream ECMP path { <list>
<t>Retrieve output interface from the NHLFE entry.</t>
<t>/* Note: this return code is set even if
Label-stack-depth is one */</t>
<t>If the output interface is not MPLS enabled { <list>
<t>Set Best-return-code to Return Code 9, "Label
switched but no MPLS forwarding at stack-depth" and
set Best-rtn-subcode to Label-stack-depth and goto
Send_Reply_Packet.</t>
</list></t>
<t>}</t>
<t>If a Downstream Detailed Mapping TLV is present { <list>
<t>A Downstream Detailed Mapping TLV SHOULD be included in the
echo reply (see <xref target='ddm'/>) filled in with
information about the current ECMP path.</t>
</list></t>
<t>}</t>
</list></t>
<t>}</t>
<t>If no Downstream Detailed Mapping TLV is present, or the Downstream
IP Address is set to the ALLROUTERS multicast address, go to
step 7 (Send Reply Packet).</t>
<t>If the "Validate FEC Stack" flag is not set and the LSR is
not configured to perform FEC checking by default, go to step
7 (Send Reply Packet).</t>
<t>/* Validate the Target FEC Stack in the received echo
request.</t>
<t>First determine FEC-stack-depth from the Downstream Detailed Mapping
TLV. This is done by walking through Stack-D (the Downstream
labels) from the bottom, decrementing the number of labels for
each non-Implicit Null label, while incrementing
FEC-stack-depth for each label. If the Downstream Detailed Mapping TLV
contains one or more Implicit Null labels, FEC-stack-depth may
be greater than Label-stack-depth. To be consistent with the
above stack-depths, the bottom is considered to be entry 1.</t>
<?rfc subcompact="yes"?>
<t>*/</t>
<t/>
<t>Set FEC-stack-depth to 0. Set i to Label-stack-depth.</t>
<t/>
<t>While (i > 0) do { <list hangIndent="4" style="hanging">
<t>++FEC-stack-depth.</t>
<t>if Stack-D [ FEC-stack-depth ] != 3 (Implicit Null)</t>
<t hangText=" ">--i.</t>
</list></t>
<t>}</t>
<t/>
<t>If the number of FECs in the FEC stack is greater than or
equal to FEC-stack-depth {</t>
<t>Perform the FEC Checking procedure (see subsection 4.4.1
below). <list>
<t>If FEC-status is 2, set Best-return-code to 10
("Mapping for this FEC is not the given label at
stack-depth").</t>
<t/>
<t>If the return code is 1, set Best-return-code to
FEC-return-code and Best-rtn-subcode to
FEC-stack-depth.</t>
</list></t>
<t>}</t>
<t/>
<t>Go to step 7 (Send Reply Packet).</t>
</list></t>
<t>}</t>
</list></t>
<?rfc subcompact="no"?>
<t><list counter="my_count" style="format %d.">
<t>Egress Processing:</t>
</list></t>
<t><list>
<t>/* These steps are performed by the LSR that identified itself
as the tail-end LSR for an LSP. */</t>
<t>If received echo request contains no Downstream Detailed Mapping TLV, or
the Downstream IP Address is set to 127.0.0.1 or 0::1 go to step 6
(Egress FEC Validation).</t>
<t>Verify that the IP address, interface address, and label stack
in the Downstream Detailed Mapping TLV match Interface-I and Stack-R. If
not, set Best-return-code to 5, "Downstream Mapping Mis-match". A
Received Interface and Label Stack TLV SHOULD be created for the
echo response packet. Go to step 7 (Send Reply Packet).</t>
</list></t>
<t><list counter="my_count" style="format %d.">
<t>Egress FEC Validation:</t>
</list></t>
<t><list>
<t>/* This is a loop for all entries in the Target FEC Stack
starting with FEC-stack-depth. */</t>
<t>Perform FEC checking by following the algorithm described in
subsection 4.4.1 for Label-L and the FEC at FEC-stack-depth.</t>
<t>Set Best-return-code to FEC-code and Best-rtn-subcode to the
value in FEC-stack-depth.</t>
<t/>
<?rfc subcompact="yes"?>
<t>If FEC-status (the result of the check) is 1,</t>
<t> go to step 7 (Send Reply Packet).</t>
<?rfc subcompact="no"?>
<t>/* Iterate to the next FEC entry */</t>
<t/>
<?rfc subcompact="yes"?>
<t>++FEC-stack-depth.</t>
<t>If FEC-stack-depth > the number of FECs in the
FEC-stack,</t>
<t> go to step 7 (Send Reply Packet).</t>
<t/>
<t>If FEC-status is 0 { <list>
<t>++Label-stack-depth.</t>
<t>If Label-stack-depth > the number of labels in
Stack-R,</t>
<t>Go to step 7 (Send Reply Packet).</t>
<t/>
<t>Label-L = extracted label from Stack-R at depth</t>
<t>Label-stack-depth.</t>
<t>Loop back to step 6 (Egress FEC Validation).</t>
</list></t>
<t>} <?rfc subcompact="no"?></t>
</list></t>
<t><list counter="my_count" style="format %d.">
<t>Send Reply Packet:</t>
</list></t>
<t><list>
<t>Send an MPLS echo reply with a Return Code of Best-return-code,
and a Return Subcode of Best-rtn-subcode. Include any TLVs created
during the above process. The procedures for sending the echo
reply are found in subsection 4.5.</t>
</list></t>
<section title=" FEC Validation">
<t>/* This subsection describes validation of an FEC entry within
the Target FEC Stack and accepts an FEC, Label-L, and Interface-I.
</t>
<t>If the outermost FEC of the target FEC stack is the Nil FEC, then the
node MUST skip the target FEC validation completely. This is to support
FEC hiding, in which the outer hidden FEC can be the Nil FEC. Else, the
algorithm performs the following steps. */ <list style="numbers">
<t>Two return values, FEC-status and FEC-return-code, are
initialized to 0.</t>
<t>If the FEC is the Nil FEC { <list style="hanging">
<?rfc subcompact="yes"?>
<t>If Label-L is either Explicit_Null or Router_Alert,
return.</t>
<t/>
<t>Else { <list style="empty">
<t>Set FEC-return-code to 10 ("Mapping for this FEC is
not the given label at stack-depth").</t>
<t>Set FEC-status to 1</t>
<t>Return.</t>
</list></t>
<t>}</t>
<?rfc subcompact="no"?>
</list> }</t>
<t>Check the FEC label mapping that describes how traffic
received on the LSP is further switched or which application it
is associated with. If no mapping exists, set FEC-return-code to
Return 4, "Replying router has no mapping for the FEC at
stack-depth". Set FEC-status to 1. Return.</t>
<t>If the label mapping for FEC is Implicit Null, set FEC-status
to 2 and proceed to step 5. Otherwise, if the label mapping for
FEC is Label-L, proceed to step 5. Otherwise, set
FEC-return-code to 10 ("Mapping for this FEC is not the given
label at stack-depth"), set FEC-status to 1, and return.</t>
<t>This is a protocol check. Check what protocol would be used
to advertise FEC. If it can be determined that no protocol
associated with Interface-I would have advertised an FEC of that
FEC-Type, set FEC-return-code to 12 ("Protocol not associated
with interface at FEC stack-depth"). Set FEC-status to 1.</t>
<t>Return.</t>
</list></t>
</section>
</section>
<section title=" Sending an MPLS Echo Reply">
<t>An MPLS echo reply is a UDP packet. It MUST ONLY be sent in
response to an MPLS echo request. The source IP address is a routable
address of the replier; the source port is the well-known UDP port for
LSP ping. The destination IP address and UDP port are copied from the
source IP address and UDP port of the echo request. The IP TTL is set
to 255. If the Reply Mode in the echo request is "Reply via an IPv4
UDP packet with Router Alert", then the IP header MUST contain the
Router Alert IP option of value 0x0 <xref target="RFC2113" /> for IPv4 or 69
<xref target="RFC7506" /> for IPv6.
If the reply is sent over an LSP, the topmost
label MUST in this case be the Router Alert label (1) (see <xref
target="RFC3032"/>).</t>
<t>The format of the echo reply is the same as the echo request. The
Sender's Handle, the Sequence Number, and TimeStamp Sent are copied
from the echo request; the TimeStamp Received is set to the
time-of-day that the echo request is received (note that this
information is most useful if the time-of-day clocks on the requester
and the replier are synchronized). The FEC Stack TLV from the echo
request MAY be copied to the reply.</t>
<t>The replier MUST fill in the Return Code and Subcode, as determined
in the previous subsection.</t>
<t>If the echo request contains a Pad TLV, the replier MUST interpret
the first octet for instructions regarding how to reply.</t>
<t>If the replying router is the destination of the FEC, then
Downstream Detailed Mapping TLVs SHOULD NOT be included in the echo reply.</t>
<t>If the echo request contains a Downstream Detailed Mapping TLV, and the
replying router is not the destination of the FEC, the replier SHOULD
compute its downstream routers and corresponding labels for the
incoming label, and add Downstream Detailed Mapping TLVs for each one to the
echo reply it sends back. A replying node should follow the procedures defined in
section 4.5.1 if there is an FEC stack change due to tunneled LSP. If the FEC stack
change is due to stitched LSP, it should follow the procedures defined in section
4.5.2</t>
<t>If the Downstream Detailed Mapping TLV contains Multipath Information
requiring more processing than the receiving router is willing to
perform, the responding router MAY choose to respond with only a
subset of multipaths contained in the echo request Downstream Detailed Mapping.
(Note: The originator of the echo request MAY send another echo
request with the Multipath Information that was not included in the
reply.)
</t>
<t>Except in the case of Reply Mode 4, "Reply via application level
control channel", echo replies are always sent in the context of the
IP/MPLS network.</t>
<section title="Addition of a New Tunnel">
<t>A transit node knows when the FEC being traced is going to enter a
tunnel at that node. Thus, it knows about the new outer FEC. All transit
nodes that are the origination point of a new tunnel SHOULD add the FEC
stack change sub-TLV
(<xref target="S3313-6424" />) to the Downstream Detailed Mapping TLV
in the echo reply. The transit node SHOULD add one FEC stack change
sub-TLV of operation type PUSH, per new tunnel being originated at
the transit node.
</t>
<t>A transit node that sends a Downstream FEC stack change sub-TLV in
the echo reply SHOULD fill the address of the remote peer; which is
the peer of the current LSP being traced. If the transit node does
not know the address of the remote peer, it MUST set the address type
to Unspecified.
</t>
<t>The Label stack sub-TLV MUST contain one additional label per FEC
being PUSHed. The label MUST be encoded as defined in
<xref target="S3312-6424" />. The label value MUST be the value used to
switch the data traffic. If the tunnel is a transparent pipe to the node,
i.e. the data-plane trace will not expire in the middle of the new tunnel,
then a FEC stack change sub-TLV SHOULD NOT be added and the Label stack
sub-TLV SHOULD NOT contain a label corresponding to the hidden tunnel.
</t>
<t>If the transit node wishes to hide the nature of the tunnel from the
ingress of the echo request, then it MAY not want to send details about
the new tunnel FEC to the ingress. In such a case, the transit node SHOULD
use the Nil FEC. The echo reply would then contain a FEC stack change
sub-TLV with operation type PUSH and a Nil FEC. The value of the label
in the Nil FEC MUST be set to zero. The remote peer address type MUST be
set to Unspecified. The transit node SHOULD add one FEC stack change
sub-TLV of operation type PUSH, per new tunnel being originated at the
transit node. The Label stack sub-TLV MUST contain one additional label
per FEC being PUSHed. The label value MUST be the value used to switch
the data traffic.
</t>
</section>
<section title="Transition between Tunnels">
<t>A transit node stitching two LSPs SHOULD include two FEC stack change
sub-TLVs. One with a POP operation for the old FEC (ingress) and one with the PUSH
operation for the new FEC (egress). The replying node SHOULD set the
Return Code to "Label switched with FEC change" to indicate change in FEC
being traced.
</t>
<t>If the replying node wishes to perform FEC hiding, it SHOULD respond
back with two FEC stack change sub-TLVs, one POP followed by one PUSH.
The POP operation MAY either exclude the FEC TLV (by setting the FEC TLV
length to 0) or set the FEC TLV to contain the LDP FEC. The PUSH
operation SHOULD have the FEC TLV containing the Nil FEC. The Return
Code SHOULD be set to "Label switched with FEC change".
</t>
<t>If the replying node wishes to perform FEC hiding, it MAY choose to not
send any FEC stack change sub-TLVs in the echo reply if the number of labels
does not change for the downstream node and the FEC type also does not
change (Nil FEC). In such case, the replying node MUST NOT set the Return
Code to "Label switched with FEC change".
</t>
</section>
</section>
<section title=" Receiving an MPLS Echo Reply">
<t>An LSR X should only receive an MPLS echo reply in response to an
MPLS echo request that it sent. Thus, on receipt of an MPLS echo
reply, X should parse the packet to ensure that it is well-formed,
then attempt to match up the echo reply with an echo request that it
had previously sent, using the destination UDP port and the Sender's
Handle. If no match is found, then X jettisons the echo reply;
otherwise, it checks the Sequence Number to see if it matches.</t>
<t>If the echo reply contains Downstream Detailed Mappings, and X wishes to
traceroute further, it SHOULD copy the Downstream Detailed Mapping(s) into its
next echo request(s) (with TTL incremented by one).</t>
<t>If one or more FEC stack change sub-TLVs are received in the MPLS echo
reply, the ingress node SHOULD process them and perform some validation.
</t>
<t>The FEC stack changes are associated with a downstream neighbor and
along a particular path of the LSP. Consequently, the ingress will
need to maintain a FEC stack per path being traced (in case of multipath).
All changes to the FEC stack resulting from the processing of FEC stack change
sub-TLV(s) should be applied only for the path along a given downstream neighbor.
The following algorithm should be followed for processing FEC stack change sub-TLVs.
</t>
<figure>
<artwork><![CDATA[
push_seen = FALSE
fec_stack_depth = current-depth-of-fec-stack-being-traced
saved_fec_stack = current_fec_stack
while (sub-tlv = get_next_sub_tlv(downstream_detailed_map_tlv))
if (sub-tlv == NULL) break
if (sub-tlv.type == FEC-Stack-Change) {
if (sub-tlv.operation == POP) {
if (push_seen) {
Drop the echo reply
current_fec_stack = saved_fec_stack
return
}
if (fec_stack_depth == 0) {
Drop the echo reply
current_fec_stack = saved_fec_stack
return
}
Pop FEC from FEC stack being traced
fec_stack_depth--;
}
if (sub-tlv.operation == PUSH) {
push_seen = 1
Push FEC on FEC stack being traced
fec_stack_depth++;
}
}
}
if (fec_stack_depth == 0) {
Drop the echo reply
current_fec_stack = saved_fec_stack
return
}
]]></artwork>
</figure>
<t>The next MPLS echo request along the same path should use the modified FEC
stack obtained after processing the FEC stack change sub-TLVs. A non-Nil FEC
guarantees that the next echo request along the same path will have the
Downstream Detailed Mapping TLV validated for IP address, Interface address,
and label stack mismatches.
</t>
<t> If the top of the FEC stack is a Nil FEC and the MPLS echo reply does
not contain any FEC stack change sub-TLVs, then it does not necessarily mean
that the LSP has not started traversing a different tunnel. It could be that
the LSP associated with the Nil FEC terminated at a transit node and at the
same time a new LSP started at the same transit node. The Nil FEC would now
be associated with the new LSP (and the ingress has no way of knowing this).
Thus, it is not possible to build an accurate hierarchical LSP topology if a
traceroute contains Nil FECs.
</t>
<t>A reply from a downstream node with Return Code 3, may not necessarily be
for the FEC being traced. It could be for one of the new FECs that was added.
On receipt of an IS_EGRESS reply, the LSP ingress should check if the depth of
Target FEC sent to the node that just responded, was the same as the depth of
the FEC that was being traced. If it was not, then it should pop an entry from
the Target FEC stack and resend the request with the same TTL (as previously sent).
The process of popping a FEC is to be repeated until either the LSP ingress receives
a non-IS_EGRESS reply or until all the additional FECs added to the FEC stack
have already been popped. Using an IS_EGRESS reply, an ingress can build a map
of the hierarchical LSP structure traversed by a given FEC.
</t>
<t>When the MPLS echo reply Return Code is "Label switched with FEC
change", the ingress node SHOULD manipulate the FEC
stack as per the FEC stack change sub-TLVs contained in the
downstream detailed mapping TLV. A transit node can use this Return
Code for stitched LSPs and for hierarchical LSPs. In case of ECMP or
P2MP, there could be multiple paths and Downstream Detailed Mapping
TLVs with different Return Codes (Section 3.2.1). The ingress node
should build the topology based on the Return Code per ECMP path/P2MP
branch.
</t>
</section>
<section title=" Issue with VPN IPv4 and IPv6 Prefixes">
<t>Typically, an LSP ping for a VPN IPv4 prefix or VPN IPv6 prefix is
sent with a label stack of depth greater than 1, with the innermost
label having a TTL of 1. This is to terminate the ping at the egress
PE, before it gets sent to the customer device. However, under certain
circumstances, the label stack can shrink to a single label before the
ping hits the egress PE; this will result in the ping terminating
prematurely. One such scenario is a multi-AS Carrier's Carrier
VPN.</t>
<t>To get around this problem, one approach is for the LSR that
receives such a ping to realize that the ping terminated prematurely,
and send back error code 13. In that case, the initiating LSR can
retry the ping after incrementing the TTL on the VPN label. In this
fashion, the ingress LSR will sequentially try TTL values until it
finds one that allows the VPN ping to reach the egress PE.</t>
</section>
<section title=" Non-compliant Routers">
<t>If the egress for the FEC Stack being pinged does not support MPLS
ping, then no reply will be sent, resulting in possible "false
negatives". If in "traceroute" mode, a transit LSR does not support
LSP ping, then no reply will be forthcoming from that LSR for some
TTL, say, n. The LSR originating the echo request SHOULD try sending
the echo request with TTL=n+1, n+2, ..., n+k to probe LSRs further
down the path. In such a case, the echo request for TTL > n SHOULD
be sent with Downstream Detailed Mapping TLV "Downstream IP Address" field set
to the ALLROUTERs multicast address until a reply is received with a
Downstream Detailed Mapping TLV. The label stack TLV MAY be omitted from the
Downstream Detailed Mapping TLV. Furthermore, the "Validate FEC Stack" flag
SHOULD NOT be set until an echo reply packet with a Downstream Detailed Mapping
TLV is received.</t>
</section>
</section>
<section title=" Security Considerations">
<t>Overall, the security needs for LSP ping are similar to those of ICMP
ping.</t>
<t>There are at least three approaches to attacking LSRs using the
mechanisms defined here. One is a Denial-of-Service attack, by sending
MPLS echo requests/replies to LSRs and thereby increasing their
workload. The second is obfuscating the state of the MPLS data plane
liveness by spoofing, hijacking, replaying, or otherwise tampering with
MPLS echo requests and replies. The third is an unauthorized source
using an LSP ping to obtain information about the network.
</t><t>
To avoid
potential Denial-of-Service attacks, it is RECOMMENDED that
implementations regulate the LSP ping traffic going to the control
plane. A rate limiter SHOULD be applied to the well-known UDP port
defined below.</t>
<t>Unsophisticated replay and spoofing attacks involving faking or
replaying MPLS echo reply messages are unlikely to be effective. These
replies would have to match the Sender's Handle and Sequence Number of
an outstanding MPLS echo request message. A non-matching replay would be
discarded as the sequence has moved on, thus a spoof has only a small
window of opportunity. However, to provide a stronger defense, an
implementation MAY also validate the TimeStamp Sent by requiring an
exact match on this field.</t>
<t>To protect against unauthorized sources using MPLS echo request
messages to obtain network information, it is RECOMMENDED that
implementations provide a means of checking the source addresses of MPLS
echo request messages against an access list before accepting the
message.</t>
<t>It is not clear how to prevent hijacking (non-delivery) of echo
requests or replies; however, if these messages are indeed hijacked, LSP
ping will report that the data plane is not working as it should.</t>
<t>It does not seem vital (at this point) to secure the data carried in
MPLS echo requests and replies, although knowledge of the state of the
MPLS data plane may be considered confidential by some. Implementations
SHOULD, however, provide a means of filtering the addresses to which
echo reply messages may be sent.</t>
<t>Although this document makes special use of 127/8 address, these are
used only in conjunction with the UDP port 3503. Furthermore, these
packets are only processed by routers. All other hosts MUST treat all
packets with a destination address in the range 127/8 in accordance to
RFC 1122. Any packet received by a router with a destination address in
the range 127/8 without a destination UDP port of 3503 MUST be treated
in accordance to RFC 1812. In particular, the default behavior is to
treat packets destined to a 127/8 address as "martians".</t>
<t>If a network operator wants to prevent tracing inside a tunnel,
one can use the Pipe Model <xref target="RFC3443" />, i.e., hide the outer MPLS
tunnel by not propagating the MPLS TTL into the outer tunnel (at
the start of the outer tunnel). By doing this, MPLS traceroute
packets will not expire in the outer tunnel and the outer tunnel
will not get traced.
</t>
<t>If one doesn't wish to expose the details of the new outer LSP,
then the Nil FEC can be used to hide those details. Using the
Nil FEC ensures that the trace progresses without false negatives
and all transit nodes (of the new outer tunnel) perform some
minimal validations on the received MPLS echo requests.
</t>
</section>
<section title="IANA Considerations">
<section title="TCP and UDP Port Number">
<t>The TCP and UDP port number 3503 has been allocated by IANA for LSP
echo requests and replies.</t>
</section>
<section title="MPLS LSP Ping Parameters">
<t>IANA maintains all the
registries within the "Multi-Protocol Label Switching
(MPLS) Label Switched Paths (LSPs) Ping Parameters" at <xref
target="IANA-MPLS-LSP-PING" />.</t>
<t>The following sub-sections detail the name spaces managed by
IANA. For some of these name spaces, the space is divided into
assignment ranges; the following terms are used in describing the
procedures by which IANA allocates values: "Standards Action" (as
defined in <xref target="RFC5226"/>), "Specification Required", and "Vendor
Private Use".</t>
<t>Values from "Specification Required" ranges MUST be registered with
IANA. The request MUST be made via an Experimental RFC that describes
the format and procedures for using the code point; the actual
assignment is made during the IANA actions for the RFC.</t>
<t>Values from "Vendor Private" ranges MUST NOT be registered with IANA;
however, the message MUST contain an enterprise code as registered with
the IANA SMI Private Network Management Private Enterprise Numbers. For
each name space that has a Vendor Private range, it must be specified
where exactly the SMI Private Enterprise Number resides; see below for
examples. In this way, several enterprises (vendors) can use the same
code point without fear of collision.</t>
<section title=" Message Types, Reply Modes, Return Codes">
<t>The IANA has created and will maintain registries for Message
Types, Reply Modes, and Return Codes. Each of these can take values in
the range 0-255. Assignments in the range 0-191 are via Standards
Action; assignments in the range 192-251 are made via "Specification
Required"; values in the range 252-255 are for Vendor Private Use, and
MUST NOT be allocated.</t>
<t>If any of these fields fall in the Vendor Private range, a
top-level Vendor Enterprise Number TLV MUST be present in the
message.</t>
<t>Message Types defined in this document are the following:</t>
<figure>
<artwork><![CDATA[
Value Meaning
----- -------
1 MPLS echo request
2 MPLS echo reply
]]></artwork>
</figure>
<t>Reply Modes defined in this document are the following:</t>
<figure>
<artwork><![CDATA[
Value Meaning
----- -------
1 Do not reply
2 Reply via an IPv4/IPv6 UDP packet
3 Reply via an IPv4/IPv6 UDP packet with Router Alert
4 Reply via application level control channel
]]></artwork>
</figure>
<t/>
<t>Return Codes defined in this document are listed in section
3.1.</t>
<t>IANA is requested to update the Reference to all these values to point to this document.</t>
</section>
<section title=" TLVs">
<t>The IANA has created and maintains a registry for the Type
field of top-level TLVs as well as for any associated sub-TLVs. Note
the meaning of a sub-TLV is scoped by the TLV. The number spaces for
the sub-TLVs of various TLVs are independent.</t>
<t>The valid range for TLVs and sub-TLVs is 0-65535. Assignments in
the range 0-16383 and 32768-49161 are made via Standards Action as
defined in <xref target="RFC5226"/>; assignments in the range 16384-31743
and 49162-64511 are made via "Specification Required" as defined
above; values in the range 31744-32767 and 64512-65535 are for Vendor
Private Use, and MUST NOT be allocated.</t>
<t>If a TLV or sub-TLV has a Type that falls in the range for Vendor
Private Use, the Length MUST be at least 4, and the first four octets
MUST be that vendor's SMI Private Enterprise Number, in network octet
order. The rest of the Value field is private to the vendor.
</t><t>
TLVs and
sub-TLVs defined in this document are the following:</t>
<figure>
<artwork><![CDATA[
Type Sub-Type Value Field
---- -------- -----------
1 Target FEC Stack
1 LDP IPv4 prefix
2 LDP IPv6 prefix
3 RSVP IPv4 LSP
4 RSVP IPv6 LSP
5 Not Assigned
6 VPN IPv4 prefix
7 VPN IPv6 prefix
8 L2 VPN endpoint
9 "FEC 128" Pseudowire - IPv4 (Deprecated)
10 "FEC 128" Pseudowire - IPv4
11 "FEC 129" Pseudowire - IPv4
12 BGP labeled IPv4 prefix
13 BGP labeled IPv6 prefix
14 Generic IPv4 prefix
15 Generic IPv6 prefix
16 Nil FEC
24 "FEC 128" Pseudowire - IPv6
25 "FEC 129" Pseudowire - IPv6
2 Downstream Mapping (Deprecated)
3 Pad
4 Not Assigned
5 Vendor Enterprise Number
6 Not Assigned
7 Interface and Label Stack
8 Not Assigned
9 Errored TLVs
Any value The TLV not understood
10 Reply TOS Byte
20 Downstream Detailed Mapping
]]></artwork>
</figure>
<t>IANA is requested to update the Reference to all these values to point to this document.</t>
</section>
<section title="Global Flags">
<t>
IANA has created a sub-registry of the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
registry. The sub-registry is called the "Global Flags" registry.
</t><t>
This registry tracks the assignment of 16 flags in the Global Flags
field of the MPLS LSP ping echo request message. The flags are
numbered from 0 (most significant bit, transmitted first) to 15.
</t><t>
New entries are assigned by Standards Action.
</t><t>
Initial entries in the registry are as follows:
</t>
<figure><artwork><![CDATA[
Bit number | Name | Reference
------------+----------------------------+--------------
15 | V Flag | This Document
14 | T Flag | [RFC6425]
13 | R Flag | [RFC6426]
12-0 | Unassigned | This Document
]]></artwork>
</figure>
</section>
<section title="Downstream Detailed Mapping Address Type">
<t>
This document extends RFC 4379 by defining a new address type for use
with the Downstream Mapping and Downstream Detailed Mapping TLVs.
IANA has established a
registry to assign address types for use
with the Downstream Mapping and Downstream Detailed Mapping TLVs,
initially allocates the following assignments:
</t>
<figure align="left"><preamble></preamble><artwork align="left"><![CDATA[
Type # Address Type K Octets Reference
------ ------------ -------- -------------------------
1 IPv4 Numbered 16 This document
2 IPv4 Unnumbered 16 This document
3 IPv6 Numbered 40 This document
4 IPv6 Unnumbered 28 This document
5 Non IP 12 RFC 6426
Downstream Mapping Address Type Registry
]]></artwork>
</figure>
<t>
Because the field in this case is an 8-bit field, the allocation
policy for this registry is "Standards Action."
</t>
</section>
<section anchor="DS_Flags" title="DS Flags">
<t>This document defines the Downstream Mapping (DSMAP) TLV and the Downstream Detailed Mapping (DDMAP) TLV, which
have Type 2 and Type 20 respectively assigned from the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry.
</t>
<t>DSMAP has been deprecated by DDMAP, but both TLVs share a field: DS Flags.</t>
<t>IANA has created and now maintains a
registry entitled "DS Flags".</t>
<t>The registration policy for this registry is
Standards Action <xref target="RFC5226"/>.</t>
<t>IANA has made the following initial assignments:
</t>
<figure align="left"><preamble></preamble><artwork align="left"> <![CDATA[
Registry Name: DS Flags
Bit number Name Reference
---------- ---------------------------------------- ---------
7 N: Treat as a Non-IP Packet This RFC
6 I: Interface and Label Stack Object Request This RFC
5-0 Unassigned]]>
]]</artwork></figure>
</section>
<section anchor="Multipath_Type" title="Multipath
Types">
<t>IANA has created and now maintains a
registry entitled "Multipath Types".</t>
<t>The registration policies <xref
target="RFC5226"/> for this registry are as follows:</t>
<t>
<figure align="left"><preamble></preamble><artwork align="left"> <![CDATA[
0-250 Standards Action
251-254 Experimental Use
255 Standards Action
]]>
</artwork></figure>
</t>
<t>IANA has made the following initial assignments:</t>
<t>
<figure align="left"><preamble></preamble><artwork align="left"> <![CDATA[
Registry Name: Multipath Types
Value Meaning Reference
---------- ---------------------------------------- ---------
0 no multipath This document
1 Unassigned
2 IP address This document
3 Unassigned
4 IP address range This document
5-7 Unassigned
8 Bit-masked IP address set This document
9 Bit-masked label set This document
10-250 Unassigned
251-254 Experimental Use This document
255 Reserved This document
]]>
</artwork></figure>
</t>
</section>
<section anchor="Pad_Type" title="Pad Type">
<t>IANA has created and now maintain a
registry entitled "Pad Types".</t>
<t>The registration policies <xref target="RFC5226"/> for this registry are:</t>
<t> <figure align="left"><preamble></preamble><artwork align="left"> <![CDATA[
0-250 Standards Action
251-254 Experimental Use
255 Standards Action
]]>
</artwork></figure></t>
<t>IANA has made the following initial assignments:</t>
<t> <figure align="left"><preamble></preamble><artwork align="left"> <![CDATA[
Registry Name: Pad Types
Value Meaning Reference
---------- ---------------------------------------- ---------
0 Reserved This document
1 Drop Pad TLV from reply This document
2 Copy Pad TLV to reply This document
3-250 Unassigned
251-254 Experimental Use This document
255 Reserved This document
]]>
</artwork></figure></t>
</section>
<section anchor="Interface_and_Label_Stack" title="Interface and Label Stack Address Type">
<t>IANA has created and now maintains a registry entitled "Interface and Label
Stack Address Types".</t>
<t>The registration policies <xref target="RFC5226"/> for this registry are:</t>
<t><figure align="left"><preamble></preamble><artwork align="left"> <![CDATA[
0-250 Standards Action
251-254 Experimental Use
255 Standards Action
]]>
</artwork></figure></t>
<t>IANA has made the following initial assignments:</t>
<t><figure align="left"><preamble></preamble><artwork align="left"> <![CDATA[
Registry Name: Interface and Label Stack Address Types
Value Meaning Reference
---------- ---------------------------------------- ---------
0 Reserved This document
1 IPv4 Numbered This document
2 IPv4 Unnumbered This document
3 IPv6 Numbered This document
4 IPv6 Unnumbered This document
5-250 Unassigned
251-254 Experimental Use This document
255 Reserved This document
]]>
</artwork></figure></t>
</section>
</section>
</section>
<section title=" Acknowledgements">
<t>The original acknowledgements from RFC 4379 state the following:
<list style="empty">
<t>This document is the outcome of many discussions among many
people, including Manoj Leelanivas, Paul Traina, Yakov Rekhter,
Der-Hwa Gan, Brook Bailey, Eric Rosen, Ina Minei, Shivani Aggarwal,
and Vanson Lim.</t>
<t>The description of the Multipath Information sub-field of the
Downstream Mapping TLV was adapted from text suggested by Curtis
Villamizar.</t>
</list></t>
<t>We would like to thank Loa Andersson for motivating the advancement
of this bis specification.</t>
<t>We also would like to thank Alexander Vainshtein, Yimin Shen, Curtis Villamizar,
David Allan for their review and comments.</t>
</section>
</middle>
<back>
<references title=" Normative References">
&rfc4271;
&rfc5226;
&rfc2119;
&rfc3032;
&rfc5905;
&rfc1122;
&rfc1812;
&rfc4379;
&rfc2113;
&rfc7506;
&rfc6424;
</references>
<references title=" Informative References">
&rfc7537;
&rfc4026;
&rfc4365;
&rfc3107;
&rfc0792;
&rfc5036;
&rfc4447;
&rfc3209;
&rfc5085;
&rfc4761;
&rfc6829;
&rfc6425;
&rfc6426;
&rfc3443;
&rfc4461;
&rfc5462;
&rfc5331;
<reference anchor="IANA-MPLS-LSP-PING"
target="http://www.iana.org/assignments/mpls-lsp-ping-parameters">
<front>
<title>Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters</title>
<author><organization>Internet Assigned Numbers Authority (IANA)</organization></author>
<date/>
</front>
</reference>
</references>
<section title="Deprecated TLVs and sub-TLVs (Non-normative)">
<t>
This appendix describes deprecated elements, which are non-normative for an implementation.
They are included in this document for historical and informational purposes.
</t>
<section title="Target FEC Stack">
<section title="FEC 128 Pseudowire - IPv4 (Deprecated)" anchor='fec128-old'>
<t>FEC 128 (0x80) is defined in <xref target="RFC4447"/>, as are
the terms PW ID (Pseudowire ID) and PW Type (Pseudowire Type). A PW
ID is a non-zero 32-bit connection ID. The PW Type is a 15-bit
number indicating the encapsulation type. It is carried right
justified in the field below termed encapsulation type with the
high-order bit set to zero. Both of these fields are treated in this
protocol as opaque values.</t>
<t>When an FEC 128 is encoded in a label stack, the following format
is used. The value field consists of the remote PE IPv4 address (the
destination address of the targeted LDP session), the PW ID, and the
encapsulation type as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Type | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>This FEC is deprecated and is retained only for backward
compatibility. Implementations of LSP ping SHOULD accept and process
this TLV, but SHOULD send LSP ping echo requests with the new TLV
(see next section), unless explicitly configured to use the old
TLV.</t>
<t>An LSR receiving this TLV SHOULD use the source IP address of the
LSP echo request to infer the sender's PE address.</t>
</section>
</section>
<section title="Downstream Mapping (Deprecated)" anchor='dm-old'>
<t>The Downstream Mapping object is a TLV that MAY be included in an
echo request message. Only one Downstream Mapping object may appear in
an echo request. The presence of a Downstream Mapping object is a
request that Downstream Mapping objects be included in the echo reply.
If the replying router is the destination of the FEC, then a
Downstream Mapping TLV SHOULD NOT be included in the echo reply.
Otherwise the replying router SHOULD include a Downstream Mapping
object for each interface over which this FEC could be forwarded. For
a more precise definition of the notion of "downstream", see section
3.3.2, "Downstream Router and Interface".</t>
<t>The Length is K + M + 4*N octets, where M is the Multipath Length,
and N is the number of Downstream Labels. Values for K are found in
the description of Address Type below. The Value field of a Downstream
Mapping has the following format:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU | Address Type | DS Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream IP Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Interface Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multipath Type| Depth Limit | Multipath Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. (Multipath Information) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Maximum Transmission Unit (MTU) <list>
<t>The MTU is the size in octets of the largest MPLS frame
(including label stack) that fits on the interface to the
Downstream LSR.</t>
</list></t>
<t>Address Type <list>
<t>The Address Type indicates if the interface is numbered or
unnumbered. It also determines the length of the Downstream IP
Address and Downstream Interface fields. The resulting total for
the initial part of the TLV is listed in the table below as "K
Octets". The Address Type is set to one of the following
values:</t>
</list></t>
<figure>
<artwork><![CDATA[
Type # Address Type K Octets
------ ------------ --------
1 IPv4 Numbered 16
2 IPv4 Unnumbered 16
3 IPv6 Numbered 40
4 IPv6 Unnumbered 28
]]></artwork>
</figure>
<t>DS Flags <list>
<t>The DS Flags field is a bit vector with the following
format:</t>
</list></t>
<figure>
<artwork><![CDATA[
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Rsvd(MBZ) |I|N|
+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Two flags are defined currently, I and N. The remaining flags MUST
be set to zero when sending and ignored on receipt.</t>
<figure>
<artwork><![CDATA[
Flag Name and Meaning
---- ----------------
I Interface and Label Stack Object Request
When this flag is set, it indicates that the replying
router SHOULD include an Interface and Label Stack
Object in the echo reply message.
N Treat as a Non-IP Packet
Echo request messages will be used to diagnose non-IP
flows. However, these messages are carried in IP
packets. For a router that alters its ECMP algorithm
based on the FEC or deep packet examination, this flag
requests that the router treat this as it would if the
determination of an IP payload had failed.
]]></artwork>
</figure>
<t>Downstream IP Address and Downstream Interface Address <list>
<t>IPv4 addresses and interface indices are encoded in 4 octets;
IPv6 addresses are encoded in 16 octets.</t>
<t>If the interface to the downstream LSR is numbered, then the
Address Type MUST be set to IPv4 or IPv6, the Downstream IP
Address MUST be set to either the downstream LSR's Router ID or
the interface address of the downstream LSR, and the Downstream
Interface Address MUST be set to the downstream LSR's interface
address.</t>
<t>If the interface to the downstream LSR is unnumbered, the
Address Type MUST be IPv4 Unnumbered or IPv6 Unnumbered, the
Downstream IP Address MUST be the downstream LSR's Router ID, and
the Downstream Interface Address MUST be set to the index assigned
by the upstream LSR to the interface.</t>
<t>If an LSR does not know the IP address of its neighbor, then it
MUST set the Address Type to either IPv4 Unnumbered or IPv6
Unnumbered. For IPv4, it must set the Downstream IP Address to
127.0.0.1; for IPv6 the address is set to 0::1. In both cases, the
interface index MUST be set to 0. If an LSR receives an Echo
Request packet with either of these addresses in the Downstream IP
Address field, this indicates that it MUST bypass interface
verification but continue with label validation.</t>
<t>If the originator of an Echo Request packet wishes to obtain
Downstream Mapping information but does not know the expected
label stack, then it SHOULD set the Address Type to either IPv4
Unnumbered or IPv6 Unnumbered. For IPv4, it MUST set the
Downstream IP Address to 224.0.0.2; for IPv6 the address MUST be
set to FF02::2. In both cases, the interface index MUST be set to
0. If an LSR receives an Echo Request packet with the all-routers
multicast address, then this indicates that it MUST bypass both
interface and label stack validation, but return Downstream
Mapping TLVs using the information provided.</t>
</list></t>
<t>Multipath Type <list>
<t>The following Multipath Types are defined:</t>
</list></t>
<figure>
<artwork><![CDATA[
Key Type Multipath Information
--- ---------------- ---------------------
0 no multipath Empty (Multipath Length = 0)
2 IP address IP addresses
4 IP address range low/high address pairs
8 Bit-masked IP IP address prefix and bit mask
address set
9 Bit-masked label set Label prefix and bit mask
]]></artwork>
</figure>
<t>
<list>
<t>Type 0 indicates that all packets will be forwarded out this one
interface.</t>
<t>Types 2, 4, 8, and 9 specify that the supplied Multipath
Information will serve to exercise this path.</t>
</list>
</t>
<t>Depth Limit <list>
<t>The Depth Limit is applicable only to a label stack and is the
maximum number of labels considered in the hash; this SHOULD be
set to zero if unspecified or unlimited.</t>
</list></t>
<t>Multipath Length <list>
<t>The length in octets of the Multipath Information.</t>
</list></t>
<t>Multipath Information <list>
<t>Address or label values encoded according to the Multipath
Type. See the next section below for encoding details.</t>
</list></t>
<t>Downstream Label(s) <list>
<t>The set of labels in the label stack as it would have appeared
if this router were forwarding the packet through this interface.
Any Implicit Null labels are explicitly included. Labels are
treated as numbers, i.e., they are right justified in the
field.</t>
<t>A Downstream Label is 24 bits, in the same format as an MPLS
label minus the TTL field, i.e., the MSBit of the label is bit 0,
the LSBit is bit 19, the Traffic Class (TC) bits are bits 20-22, and bit 23 is
the S bit. The replying router SHOULD fill in the TC and S bits;
the LSR receiving the echo reply MAY choose to ignore these bits.
</t>
</list></t>
<t> Protocol <list>
<t>The Protocol is taken from the following table:</t>
</list></t>
<figure>
<artwork><![CDATA[
Protocol # Signaling Protocol
---------- ------------------
0 Unknown
1 Static
2 BGP
3 LDP
4 RSVP-TE
]]></artwork>
</figure>
<section title=" Multipath Information Encoding">
<t>The Multipath Information encodes labels or addresses that will
exercise this path. The Multipath Information depends on the
Multipath Type. The contents of the field are shown in the table
above. IPv4 addresses are drawn from the range 127/8; IPv6 addresses
are drawn from the range 0:0:0:0:0:FFFF:7F00:0/104. Labels are treated
as numbers, i.e., they are right justified in the field. For Type 4,
ranges indicated by Address pairs MUST NOT overlap and MUST be in
ascending sequence.</t>
<t>Type 8 allows a more dense encoding of IP addresses. The IP
prefix is formatted as a base IP address with the non-prefix
low-order bits set to zero. The maximum prefix length is 27.
Following the prefix is a mask of length 2^(32-prefix length) bits
for IPv4 and 2^(128-prefix length) bits for IPv6. Each bit set to 1
represents a valid address. The address is the base IPv4 address
plus the position of the bit in the mask where the bits are numbered
left to right beginning with zero. For example, the IPv4 addresses
127.2.1.0, 127.2.1.5-127.2.1.15, and 127.2.1.20-127.2.1.29 would be
encoded as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Those same addresses embedded in IPv6 would be encoded as
follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Type 9 allows a more dense encoding of labels. The label prefix
is formatted as a base label value with the non-prefix low-order
bits set to zero. The maximum prefix (including leading zeros due to
encoding) length is 27. Following the prefix is a mask of length
2^(32-prefix length) bits. Each bit set to one represents a valid
label. The label is the base label plus the position of the bit in
the mask where the bits are numbered left to right beginning with
zero. Label values of all the odd numbers between 1152 and 1279
would be encoded as follows:</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>If the received Multipath Information is non-null, the labels and
IP addresses MUST be picked from the set provided. If none of these
labels or addresses map to a particular downstream interface, then
for that interface, the type MUST be set to 0. If the received
Multipath Information is null (i.e., Multipath Length = 0, or for
Types 8 and 9, a mask of all zeros), the type MUST be set to 0.</t>
<t>For example, suppose LSR X at hop 10 has two downstream LSRs, Y
and Z, for the FEC in question. The received X could return
Multipath Type 4, with low/high IP addresses of
127.1.1.1->127.1.1.255 for downstream LSR Y and
127.2.1.1->127.2.1.255 for downstream LSR Z. The head end
reflects this information to LSR Y. Y, which has three downstream
LSRs, U, V, and W, computes that 127.1.1.1->127.1.1.127 would go
to U and 127.1.1.128-> 127.1.1.255 would go to V. Y would then
respond with 3 Downstream Mappints (or 3 "Downstream Detailed Mapping" TLVs): to U, with Multipath Type 4
(127.1.1.1->127.1.1.127); to V, with Multipath Type 4
(127.1.1.127->127.1.1.255); and to W, with Multipath Type 0.</t>
<t>Note that computing Multipath Information may impose a
significant processing burden on the receiver. A receiver MAY thus
choose to process a subset of the received prefixes. The sender, on
receiving a reply to a Downstream (Detailed) Mapping with partial information,
SHOULD assume that the prefixes missing in the reply were skipped by
the receiver, and MAY re-request information about them in a new
echo request.</t>
<t>The encoding of Multipath information in scenarios where few LSRs apply Entropy
label based load balancing while other LSRs are non-EL (IP based) load balancing
will be defined in a different document.
</t>
<t>The encoding of multipath information in scenarios where LSR have Layer 2 ECMP
over Link Aggregation Group (LAG) interfaces will be defined in different document.
</t>
</section>
<section title=" Downstream Router and Interface">
<t>The notion of "downstream router" and "downstream interface"
should be explained. Consider an LSR X. If a packet that was
originated with TTL n>1 arrived with outermost label L and TTL=1
at LSR X, X must be able to compute which LSRs could receive the
packet if it was originated with TTL=n+1, over which interface the
request would arrive and what label stack those LSRs would see. (It
is outside the scope of this document to specify how this
computation is done.) The set of these LSRs/interfaces consists of
the downstream routers/interfaces (and their corresponding labels)
for X with respect to L. Each pair of downstream router and
interface requires a separate Downstream (Detailed) Mapping to be added to the
reply.</t>
<t>The case where X is the LSR originating the echo request is a
special case. X needs to figure out what LSRs would receive the MPLS
echo request for a given FEC Stack that X originates with TTL=1.</t>
<t>The set of downstream routers at X may be alternative paths (see
the discussion below on ECMP) or simultaneous paths (e.g., for MPLS
multicast). In the former case, the Multipath Information is used as
a hint to the sender as to how it may influence the choice of these
alternatives.</t>
</section>
</section>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 11:00:19 |