One document matched: draft-kumarkini-mpls-spring-lsp-ping-02.xml
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<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
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<rfc category='std' ipr='trust200902' docName='draft-kumarkini-mpls-spring-lsp-ping-02'>
<front>
<title abbrev="LSP Ping/Trace for SR on MPLS">Label Switched Path (LSP) Ping/Trace for Segment Routing Networks Using MPLS Dataplane</title>
<author initials="N." surname="Kumar" fullname="Nagendra Kumar">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>7200 Kit Creek Road</street>
<city>Research Triangle Park</city> <region>NC</region> <code>27709</code>
<country>US</country>
</postal>
<email>naikumar@cisco.com</email>
</address>
</author>
<author initials="G." surname="Swallow" fullname="George Swallow">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>1414 Massachusetts Ave</street>
<city>Boxborough</city> <region>MA</region> <code>01719</code>
<country>US</country>
</postal>
<email>swallow@cisco.com</email>
</address>
</author>
<author initials="C." surname="Pignataro" fullname="Carlos Pignataro">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>7200 Kit Creek Road</street>
<city>Research Triangle Park</city> <region>NC</region> <code>27709-4987</code>
<country>US</country>
</postal>
<email>cpignata@cisco.com</email>
</address>
</author>
<author initials="N." surname="Akiya" fullname="Nobo Akiya">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>2000 Innovation Drive</street>
<city>Kanata</city> <region>ON</region> <code>K2K 3E8</code>
<country>Canada</country>
</postal>
<email>nobo@cisco.com</email>
</address>
</author>
<author initials="S." surname="Kini" fullname="Sriganesh Kini">
<organization>Ericsson</organization>
<address>
<postal>
<street></street>
<city></city> <region></region> <code></code>
<country></country>
</postal>
<email>sriganesh.kini@ericsson.com</email>
</address>
</author>
<author initials="H." surname="Gredler" fullname="Hannes Gredler">
<organization>Juniper Networks</organization>
<address>
<postal>
<street></street>
<city></city> <region></region> <code></code>
<country></country>
</postal>
<email>hannes@juniper.net</email>
</address>
</author>
<author fullname="Mach(Guoyi) Chen" initials="M." surname="Chen">
<organization>Huawei</organization>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country/>
</postal>
<email>mach.chen@huawei.com</email>
</address>
</author>
<date day="27" month="October" year="2014" />
<area>Internet</area>
<workgroup>Network Work group</workgroup>
<keyword>mpls</keyword>
<abstract><t>Segment Routing architecture leverages the source routing and tunneling paradigms and
can be directly applied to MPLS data plane. A node steers a packet through a
controlled set of instructions called segments, by prepending the packet with Segment
Routing header. </t>
<t> The segment assignment and forwarding semantic nature of
Segment Routing raises additional consideration for connectivity verification and
fault isolation in LSP with Segment Routing architecture. This document illustrates the problem and
describe a mechanism to perform LSP Ping and Traceroute on Segment Routing network over MPLS data plane.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t><xref target="I-D.filsfils-spring-segment-routing" /> introduces and explains
Segment Routing architecture
that leverages the source routing and tunneling paradigms. A node steers a packet through a
controlled set of instructions called segments, by prepending the packet with Segment Routing header. A
detailed definition about Segment Routing architecture is available in
<xref target="I-D.filsfils-spring-segment-routing" />
and different use-cases are discussed in
<xref target="I-D.filsfils-spring-segment-routing-use-cases" /></t>
<t>The Segment Routing architecture can be directly applied to MPLS data plane in a way that, the Segment
identifier (Segment ID) will be of 20-bits size and SR header is the label stack. </t>
<t>Multi Protocol Label Switching (MPLS) has defined in [RFC4379] a simple and efficient
mechanism to detect data plane failures in Label Switched Paths (LSP) by specifying
information to be 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.
The functionality is modeled after the ping/traceroute paradigm (ICMP echo request
<xref target="RFC0792" />) and is typically referred to as LSP ping and LSP traceroute.
</t>
<t>Unlike LDP or RSVP which are the other
well-known MPLS control plane protocols, segment assignment in Segment Routing architecture
is not hop-by-hop basis.</t>
<t>This nature of Segment Routing raises additional consideration for fault detection and
isolation in Segment Routing network. This document illustrates the problem and
describe a mechanism to perform LSP Ping and Traceroute on Segment Routing network over MPLS data plane.
</t>
</section>
<section title="Requirements notation">
<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 <xref target="RFC2119"/>.
</t>
</section>
<section title="Challenges with Existing mechanism">
<t>This document defines Target FEC Stack sub-TLVs and explains how they can be used to tackle below challenges.
</t>
<section title="Path validation in Segment Routing networks">
<t><xref target="RFC4379" /> defines the OAM machinery that helps with fault detection and
isolation in MPLS dataplane path with the use of various Target FEC
Stack Sub-TLV that are carried in MPLS Echo Request packets and used by the responder for
FEC validation. While it is obvious that new Sub-TLVs need to be assigned, the
unique nature of Segment Routing architecture raises a need for additional machinery for
path validation. This section discuss the challenges as below:
</t>
<figure>
<artwork><![CDATA[
L1
+--------+
| L2 |
R3-------R6
/ \
/ \
R1----R2 R7----R8
\ / L3
\ /
R4-------R5
Figure 1: Segment Routing network
{5001, 5002, 5003, 5004, 5005, 5006, 5007, 5008} --> Node Segment ID for R1, R2, R3 R4, R5 R6, R7, R8 respectively.
9136 --> Adjacency Segment ID from R3 to R6 over link L1.
9236 --> Adjacency Segment ID from R3 to R6 over link L2.
]]></artwork>
</figure>
<t>The forwarding semantic of Adjacency Segment ID is to pop the segment ID and send the packet to
a specific neighbor over a specific link. A malfunctioning node may forward packets using
Adjacency Segment ID to incorrect neighbor or over incorrect link. Exposed segment ID (after
incorrectly forwarded Adjacency Segment ID) might still allow such packet to reach the
intended destination, although the intended strict traversal has been broken.</t>
<t>Assume in above topology, R1 sends traffic with segment stack as {9124, 5007, 9378} so that the path taken
will be R1-R2-R4-R5-R7-R8. If the Adjacency Segment ID 9124 is misprogrammed in R2 to send the packet to R1 or R3,
it will still be delivered to R8 but is not via the expected path.
</t>
<t>MPLS traceroute may help with detecting such deviation in above mentioned scenario. However, in a different example, it may not be
helpful if R3, due to misprogramming, forwards packet with Adjacency Segment ID 9236 via link L1 while it is expected
to be forwarded over Link L2.
</t>
</section>
<section title="Service Label">
<t>A Segment ID can represent a service based instruction. An SR header can have label stack entries where
the label represents a service to be applied along the path. Since these labels
are part of the label stack, they can influence the path taken by a packet and consequently
have implications on MPLS OAM.
This document describes how the procedures of [RFC4379] can be
applied to in the absence of service-labels in Section 6.5. Additional
considerations for service labels are included in Section 7 and
requires further discussion.
</t>
</section>
</section>
<section title="Segment ID sub-TLV">
<t>The format of the following Segment ID sub-TLVs follows the philosophy of Target FEC Stack
TLV carrying FECs corresponding to each label in the label stack.
When operated with the procedures defined in <xref target="RFC4379" />, this allows LSP
ping/traceroute operations to function when Target FEC Stack TLV
contains more FECs than received label stack at responder nodes.</t>
<t>Three new sub-TLVs are defined for TLVs type 1, 16 and 21.
</t>
<figure>
<artwork><![CDATA[
sub-Type Value Field
-------- ---------------
TBD1 IPv4 Prefix Node Segment ID
TBD2 IPv6 Prefix Node Segment ID
TBD3 Adjacency Segment ID
]]></artwork>
</figure>
<t>Service Segments and FRR will be considered in future version.</t>
<section title="IPv4 Prefix Node Segment ID">
<t>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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Protocol | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>IPv4 Prefix
<list><t>This field carries the IPv4 prefix to which the Node Segment
ID is assigned.</t>
</list>
</t>
<t>Prefix Length
<list><t>The Prefix Length field is one octet, it gives the length of
the prefix in bits (values can be 1 - 32).</t>
</list>
</t>
<t>Protocol
<list><t>Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is ISIS.
</t>
</list>
</t>
</section>
<section title="IPv6 Prefix Node Segment ID">
<t>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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Protocol | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>IPv6 Prefix
<list><t>This field carries the IPv6 prefix to which the Node Segment
ID is assigned.</t>
</list>
</t>
<t>Prefix Length
<list><t>The Prefix Length field is one octet, it gives the length of
the prefix in bits (values can be 1 - 128).</t>
</list>
</t>
<t>Protocol
<list><t>Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is ISIS.
</t>
</list>
</t>
</section>
<section title="IGP Adjacency Segment ID">
<t>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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Adj. Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Advertising Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Local Interface ID
<list><t>An identifier that is assigned by local LSR for a link on which Adjacency
Segment ID is bound. This field is set to local link address (IPv4 or IPv6).
Incase of unnumbered, 32 bit link identifier defined in <xref target="RFC4203" />,
<xref target="RFC5307" /> is used.
If the Adjacency Segment ID represents parallel adjacencies (Section
3.5.1 of <xref target="I-D.filsfils-spring-segment-routing" />) this field MUST be set
to zero.
</t>
</list>
</t>
<t>Remote Interface ID
<list><t>An identifier that is assigned by remote LSR for a link on which Adjacency
Segment ID is bound. This field is set to remote (downstream neighbor)
link address (IPv4 or IPv6).
In case of unnumbered, 32 bit link identifier defined in <xref target="RFC4203" />,
<xref target="RFC5307" /> is used.
If the Adjacency Segment ID represents parallel adjacencies (Section
3.5.1 of <xref target="I-D.filsfils-spring-segment-routing" />) this field MUST be set
to zero.</t>
</list>
</t>
<t>Protocol
<list><t>Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is ISIS
</t>
</list>
</t>
<t>Adj. Type
<list><t>Set to 4, if the Local/Remote Interface ID is of 4 octets and set to
6 if the field is of 16 octets.
</t>
</list>
</t>
<t>Advertising Node Identifier
<list><t>Specifies the advertising node identifier. When Protocol is set to 1,
then the 32 rightmost bits represent OSPF Router ID and if protocol is set to
2, this field carries 48 bit ISIS System ID.</t>
</list>
</t>
</section>
</section>
<section title="Extension to Downstream Mapping TLV">
<t>In an echo reply, the Downstream Mapping TLV [RFC4379] is used to
report for each interface over which a FEC could be forwarded. For
a FEC, there are multiple protocols that may be used to distribute
label mapping. The "Protocol" field of the Downstream Mapping TLV is
used to return the protocol that is used to distribute a specific a
label. The following protocols are defined in section 3.2 of
[RFC4379]:
</t>
<figure>
<artwork><![CDATA[
Protocol # Signaling Protocol
---------- ------------------
0 Unknown
1 Static
2 BGP
3 LDP
4 RSVP-TE
]]></artwork>
</figure>
<t>With segment routing, OSPF or ISIS can be used for label
distribution, this document adds two new protocols as follows:
</t>
<figure>
<artwork><![CDATA[
Protocol # Signaling Protocol
---------- ------------------
5 OSPF
6 ISIS
]]></artwork>
</figure>
</section>
<section title="Procedures">
<t>This section describes aspects of LSP Ping and traceroute operations that require further considerations beyond <xref target="RFC4379" />.</t>
<section title="FECs in Target FEC Stack TLV">
<t>When LSP echo request packets are generated by an initiator, FECs carried in Target FEC Stack TLV may need to or desire to have deviating contents. This document outlines expected Target FEC Stack TLV construction mechanics by initiator for known scenarios.
<list>
<t>Ping
<list>
<t>Initiator MUST include FEC(s) corresponding to the destination segment.</t>
<t>Initiator MAY include FECs corresponding to some or all of segments imposed in the label stack by the initiator to communicate the segments traversed.</t>
</list>
</t>
<t>Traceroute
<list>
<t>Initiator MUST initially include FECs corresponding to all of segments imposed in the label stack.</t>
<t>When a received echo reply contains FEC Stack Change TLV with one or more of original segment(s) being popped, initiator MAY remove corresponding FEC(s) from Target FEC Stack TLV in the next (TTL+1) traceroute request.</t>
<t>When a received echo reply does not contain FEC Stack Change TLV, initiator MUST NOT attempt to remove FEC(s) from Target FEC Stack TLV in the next (TTL+1) traceroute request. Note that Downstream Label field of DSMAP/DDMAP contains hints on how initiator may be able to update the contents of next Target FEC Stack TLV. However, such hints are ambiguous without full understanding of PHP capabilities.</t>
</list>
</t>
</list>
</t>
</section>
<section title="FEC Stack Change sub-TLV">
<t>Section 3.3.1.3 of <xref target="RFC6424" /> defines a new sub-TLV that a router must include when the FEC stack changes.</t>
<t>The network node which advertised the Node Segment ID is responsible for generating FEC Stack Change sub-TLV of &pop& operation for Node Segment ID, regardless of if PHP is enabled or not.</t>
<t>The network node that is immediate downstream of the node which advertised the Adjacency Segment ID is responsible for generating FEC Stack Change sub-TLV of &pop& operation for Adjacency Segment ID.</t>
</section>
<section title="Segment ID POP Operation">
<t>The forwarding semantic of Node Segment ID with PHP flag is equivalent to usage of implicit Null in MPLS protocols.
Adjacency Segment ID is also similar in a sense that it can be thought as next hop
destined locally allocated segment that has PHP enabled. Procedures described in Section 4.4 of
<xref target="RFC4379" /> relies on Stack-D and Stack-R explicitly having Implicit Null value. It may simplify
implementations to reuse Implicit Null for Node Segment ID PHP and Adjacency Segment ID cases. However, it is
technically incorrect for Implicit Null value to externally appear. Therefore, implicit Null MUST NOT be placed
in Stack-D and Interface and Label Stack TLV for Node Segment ID PHP and Adjacency Segment ID cases.</t>
</section>
<section title="Segment ID Check">
<t>
<list>
<t>If the Target FEC Stack Sub-TLV at FEC-stack-depth is TBD1 (IPv4 Prefix Node Segment ID), the responder SHOULD set Best return code to (error code TBD) if any below conditions fail:
<list style="symbols">
<t>Validate that Node Segment ID is advertised for IPv4 Prefix.</t>
<t>Validate that Node Segment ID is advertisement of PHP bit.</t>
<t>To be Updated</t>
</list>
</t>
<t>If the Target FEC Sub-TLV at FEC-stack-depth is TBD2 (IPv6 Prefix Node Segment ID), set Best return code to (error code TBD) if any below conditions fail:
<list style="symbols">
<t>Validate that Node Segment ID is advertised for IPv6 Prefix.</t>
<t>Validate that Node Segment ID is advertised of PHP bit.</t>
<t>To be Updated</t>
</list>
</t>
<t>If the Target FEC sub-TLV at FEC-stack-depth is TBD3 (Adjacency Segment ID), set Best return code to (error code TBD) if any below conditions fail:
<list style="symbols">
<t>Validate that Remote Interface ID matches the local identifier of the interface on which the packet was received.</t>
<t>Validate that IGP Adjacency Segment ID is advertised by Advertising Node Identifier of Protocol in local IGP database.</t>
</list>
</t>
</list>
</t>
</section>
<section title="TTL Consideration for traceroute">
<t>LSP Traceroute operation can properly traverse every hop of Segment
Routing network in Uniform Model described in <xref target="RFC3443" />. If one or
more LSRs employ Short Pipe Model described in <xref target="RFC3443" />, then LSP
Traceroute may not be able to properly traverse every hop of Segment
Routing network due to absence of TTL copy operation when outer label
is popped. In such scenario, following TTL manipulation technique MAY
be used.
</t>
<t>When tracing a LSP according to the procedures in <xref target="RFC4379" /> the TTL
is incremented by one in order to trace the path sequentially along
the LSP. However when a source routed LSP has to be traced there are
as many TTLs as there are labels in the stack. The LSR that
initiates the traceroute SHOULD start by setting the TTL to 1 for the
tunnel in the LSP's label stack it wants to start the tracing from,
the TTL of all outer labels in the stack to the max value, and the
TTL of all the inner labels in the stack to zero. Thus a typical
start to the traceroute would have a TTL of 1 for the outermost label
and all the inner labels would have TTL 0. If the FEC Stack TLV is
included it should contain only those for the inner stacked tunnels.
The lack of an echo response or the Return Code/Subcode should be
used to diagnose the tunnel as described in <xref target="RFC4379" />. When the
tracing of a tunnel in the stack is complete, then the next tunnel in
the stack should be traced. The end of a tunnel can be detected from
the "Return Code" when it indicates that the responding LSR is an
egress for the stack at depth 1. Thus the traceroute procedures in
<xref target="RFC4379" /> can be recursively applied to traceroute a source routed
LSP.
</t>
</section>
</section>
<section title="Issues with non-forwarding labels">
<t>Source stacking can be optionally used to apply services on the
packet at a LSR along the path, where a label in the stack is used to
trigger service application. A data plane failure detection and
isolation mechanism should provide its functionality without applying
these services. This is mandatory for services that are stateful,
though for stateless services <xref target="RFC4379" /> could be used as-is. It MAY
also provide a mechanism to detect and isolate faults within the
service function itself.</t>
<t>To prevent services from being applied to an "echo request" packet,
the TTL of service labels MUST be 0. However TTL processing rules of
a service label must be the same as any MPLS label. Due to this a
TTL of 0 in the service label would prevent the packet from being
forwarded beyond the LSR that provides the service. To avoid this
problem, the originator of the "echo request" MUST NOT include the
service label in the label stack of an echo request above the tunnel
label of the tunnel that is being currently
traced. In other words the ingress must remove all service-labels
above the label of the tunnel being currently traced, but retain
service labels below it when sending the echo request. Note that
load balancing may affect the path when the service labels are
removed, resulting in a newer path being traversed. However this new
path is potentially different only up to the LSR that provides the
service. Since this portion of the path was traced when the tunnels
above this tunnel in the stack were traced and followed the exact
path as the source routed LSP, this should not be a major concern.
Sometimes the newer path may have a problem that was not in the
original path resulting in a false positive. In such a case the
original path can be traversed by changing the label stack to reach
the intermediate LSR with labels that route along each hop
explicitly.
</t>
</section>
<section title="IANA Considerations">
<section title="New Target FEC Stack Sub-TLVs">
<t>IANA is requested to assign 3 new Sub-TLVs from "Sub-TLVs for TLV Types 1,
16 and 21" sub-registry.
</t>
<figure>
<artwork><![CDATA[
Sub-Type Sub-TLV Name Reference
---------- ----------------- ------------
TBD1 IPv4 Prefix Node Segment ID Section 4.1 (this document)
TBD2 IPv6 Prefix Node Segment ID Section 4.2 (this document)
TBD3 Adjacency Segment ID Section 4.3 (this document)
]]></artwork>
</figure>
</section>
</section>
<section title="Security Considerations">
<t>This document defines additional Sub-TLVs and follows the mechanism defined
in <xref target="RFC4379" />. So all the security consideration defined in
<xref target="RFC4379" /> will be applicable for this document and in addition
it does not impose any security challenges to be considered.</t>
</section>
<section title="Acknowledgement">
<t> The authors would like to thank Stefano Previdi, Les Ginsberg,
Balaji Rajagopalan and Harish Sitaraman for their review
and comments.</t>
<t> The authors wold like to thank Loa Andersson for his comments and
recommendation to merge drafts.</t>
</section>
<section title="Contributing Authors">
<t>Tarek Saad
<vspace blankLines="0" />
Cisco Systems
<vspace blankLines="0" />
Email: tsaad@cisco.com</t>
<t>Siva Sivabalan
<vspace blankLines="0" />
Cisco Systems
<vspace blankLines="0" />
Email: msiva@cisco.com</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.I-D.filsfils-spring-segment-routing"?>
<?rfc include="reference.I-D.filsfils-spring-segment-routing-use-cases"?>
<?rfc include="reference.I-D.gredler-spring-mpls"?>
<?rfc include="reference.RFC.4379"?>
<?rfc include="reference.RFC.6424"?>
<?rfc include="reference.RFC.0792"?>
<?rfc include="reference.RFC.3443"?>
<?rfc include="reference.RFC.4203"?>
<?rfc include="reference.RFC.5307"?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.6425"?>
<?rfc include="reference.RFC.6291"?>
</references>
</back>
</rfc>
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