One document matched: draft-akiya-mpls-entropy-lsp-ping-03.xml
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<rfc category="std" docName="draft-akiya-mpls-entropy-lsp-ping-03" ipr="trust200902" updates="4379,6424,6790">
<!-- category values: std, bcp, info, exp, and historic
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<!-- ***** FRONT MATTER ***** -->
<front>
<title abbrev="LSP Ping over Entropy">
Label Switched Path (LSP) and Pseudowire (PW) Ping/Trace over MPLS Network using Entropy Labels (EL)
</title>
<!-- add 'role="editor"' below for the editors if appropriate -->
<!-- Another author who claims to be an editor -->
<author fullname="Nobo Akiya" initials="N."
surname="Akiya">
<organization>Cisco Systems</organization>
<address>
<email>nobo@cisco.com</email>
</address>
</author>
<author fullname="George Swallow" initials="G."
surname="Swallow">
<organization>Cisco Systems</organization>
<address>
<email>swallow@cisco.com</email>
</address>
</author>
<author fullname="Carlos Pignataro" initials="C."
surname="Pignataro">
<organization>Cisco Systems</organization>
<address>
<email>cpignata@cisco.com</email>
</address>
</author>
<author fullname="Andrew G. Malis" initials="A."
surname="Malis">
<organization>Huawei Technologies</organization>
<address>
<email>agmalis@gmail.com</email>
</address>
</author>
<author fullname="Sam Aldrin" initials="S."
surname="Aldrin">
<organization>Huawei Technologies</organization>
<address>
<email>aldrin.ietf@gmail.com</email>
</address>
</author>
<date year="2014" />
<area>MPLS Working Group</area>
<workgroup>Internet Engineering Task Force</workgroup>
<!-- WG name at the upperleft corner of the doc,
IETF is fine for individual submissions.
If this element is not present, the default is "Network Working Group",
which is used by the RFC Editor as a nod to the history of the IETF. -->
<keyword>MPLS</keyword>
<keyword>LSP Ping</keyword>
<keyword>Entropy</keyword>
<!-- Keywords will be incorporated into HTML output
files in a meta tag but they have no effect on text or nroff
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<abstract>
<t>The Multiprotocol Label Switching (MPLS) Label Switched Path
(LSP) Ping and Traceroute are used to exercise specific paths of
Equal-Cost Multipath (ECMP). When LSP is signaled to use Entropy
Label (EL) described in RFC6790, the ability for LSP
Ping and Traceroute operation to discover and exercise ECMP paths has
been lost in scenarios which LSRs apply deviating load balance
techniques. One such scenario is when some LSRs apply EL based load
balancing while other LSRs apply non-EL based load balancing (ex: IP).
Another scenario is when EL based LSP is stitched with another LSP
which can be EL based or non-EL based.
</t>
<t>This document extends the MPLS LSP Ping and Traceroute
mechanisms to restore the ability of exercising specific paths
of ECMP over LSP which make use of Entropy Label. This
document updates RFC4379, RFC6424 and RFC6790.
</t>
</abstract>
<note title="Requirements Language">
<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">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction" anchor="INTRO">
<section title="Terminology">
<t>The following acronyms/terminologies are used in this document:
<list style="symbols">
<t>MPLS - Multiprotocol Label Switching.</t>
<t>LSP - Label Switched Path.</t>
<t>LSR - Label Switching Router.</t>
<t>FEC - Forwarding Equivalent Class.</t>
<t>ECMP - Equal-Cost Multipath.</t>
<t>EL - Entropy Label.</t>
<t>ELI - Entropy Label Indicator.</t>
<t>GAL - Generic Associated Channel Label.</t>
<t>MS-PW - Multi-Segment Pseudowire.</t>
<t>Initiating LSR - LSR which sends MPLS echo request.</t>
<t>Responder LSR - LSR which receives MPLS echo request and sends MPLS echo reply.</t>
<t>IP Based Load Balancer - LSR which load balances on fields from IP header (and possibly fields from upper layers), and does not consider entropy label from label stack (i.e. Flow Label or Entropy Label) for load balancing purpose.</t>
<t>Label Based Load Balancer - LSR which load balances on entropy label from label stack (i.e. Flow Label or Entropy Label), and does not consider fields from IP header (and possibly fields from upper layers) for load balancing purpose.</t>
<t>Label and IP Based Load Balancer - LSR which load balances on both labels from label stack (including Flow Label or Entropy Label if present) and fields from IP header (and possibly fields from upper layers).</t>
</list>
</t>
</section>
<section title="Prerequisite">
<t>MPLS implementations employ wide variety of load balancing techniques in terms of fields used for hash "keys". <xref target="RFC4379" /> and <xref target="RFC6424" /> are designed to provide multipath support for subset of techniques. Intent of this document is to restore multipath support for those supported techniques which have been compromised by the introduction of <xref target="RFC6790" /> (i.e. Entropy Labels). <xref target="_CASES" /> describes supported and unsupported cases, and it may be useful for one to visit this section first.</t>
</section>
<section title="Background">
<t>Section 3.3.1 of <xref target="RFC4379" /> specifies
multipath information encoding in Downstream Mapping TLV (Section 3.3 of <xref target="RFC4379" />) and Downstream Detailed Mapping TLV (Section 3.3 of <xref target="RFC6424" />) which can be used by LSP Ping
initiator to trace and validate all ECMP paths between ingress
and egress. These encodings are sufficient when all the LSRs along
the path(s), between ingress and egress, consider same set of
"keys" as input for load balancing algorithm: all IP
based or all label based.</t>
<t>With introduction of <xref target="RFC6790" />, it is quite
normal to see set of LSRs performing load balancing based on
EL/ELI while others still follow the traditional way (IP
based). This results in LSP Ping initiator not be able to
trace and validate all ECMP paths in following scenarios:
<list style="symbols">
<t>One or more transit LSRs along LSP with ELI/EL in label
stack do not perform ECMP load balancing based on EL
(hashes based on "keys" including IP destination
address). This scenario is not only possible but quite common
due transit LSRs not implementing <xref target="RFC6790" />
or transit LSRs implementing <xref target="RFC6790" /> but
not implementing suggested transit LSR behavior in Section
4.3 of <xref target="RFC6790" />.</t>
<t>Two or more LSPs stitched together with at least one of these
LSP pushing ELI/EL in label stack. Such scenarios are described
in <xref target="I-D.ravisingh-mpls-el-for-seamless-mpls" />.
</t>
</list>
These scenarios will be quite common because every deployment
of <xref target="RFC6790" /> will invariably end up with nodes
that support ELI/EL and nodes that do not. There will
typically be areas that support ELI/EL and areas that do
not.</t>
<t>As pointed out in <xref target="RFC6790" /> the procedures of
<xref target="RFC4379" /> with respect to multipath
information type {9} are incomplete. However
<xref target="RFC6790" /> does not actually update
<xref target="RFC4379" />. Further the specific EL location
is not clearly defined, particularly in the case of Flow Aware
Pseudowires <xref target="RFC6391" />. This document
defines a new FEC Stack sub-TLV for the Entropy Label.
<xref target="MPT9-Sec" /> of this document updates the
procedures for multipath information type {9} described in
<xref target="RFC4379" />. Rest of this document describes
extensions required to restore ECMP discovery and tracing
capabilities for scenarios described.
</t>
</section>
</section>
<section title="Overview">
<t><xref target="RFC4379" /> describes LSP traceroute as an operation where the initiating LSR send a series of MPLS echo requests towards the same destination. The first packet in the series have the TTL set to 1. When the echo reply is received from the LSR one hop away the second echo request in the series is sent with the TTL set to 2, for each echo request the TLL is incremented by one until a response is received from the intended destination. Initiating LSR discovers and exercises ECMP by
obtaining multipath information from each transit LSR and using
specific destination IP address or specific entropy label.</t>
<t>Notion of {x, y, z} from here on refers to Multipath information types x, y or z.</t>
<t>LSP Ping initiating LSR sends MPLS echo request with multipath
information. This multipath information is described in
DSMAP/DDMAP TLV of echo request, and may contain set of IP
addresses or set of labels. Multipath information types
{2, 4, 8} carry set of IP addresses and multipath information
type {9} carries set of labels. Responder LSR (receiver of MPLS
echo request) will determine the subset of initiator specified
multipath information which load balances to each downstream
(outgoing interface). Responder LSR sends MPLS echo reply with
resulting multipath information per downstream (outgoing
interface) back to the initiating LSR. Initiating LSR is then able
to use specific IP destination address or specific label to
exercise specific ECMP path on the responder LSR.</t>
<t>Current behavior is problematic in following scenarios:
<list style="symbols">
<t>Initiating LSR sends IP multipath information, but
responder LSR load balances on labels.</t>
<t>Initiating LSR sends label multipath information, but
responder LSR load balances on IP addresses.</t>
<t>Initiating LSR sends existing multipath information
to LSR which pushes ELI/EL in label stack, but the initiating
LSR can only continue to discover and exercise specific
path of ECMP, if the LSR which pushes ELI/EL responds with both
IP addresses and associated EL corresponding to each IP
address. This is because:
<list style="symbols">
<t>ELI/EL pushing LSR that is a stitching point will
load balance based on IP address.</t>
<t>Downstream LSR(s) of ELI/EL pushing LSR may load
balance based on ELs.</t>
</list>
</t>
<t>Initiating LSR sends one of existing multipath information
to ELI/EL pushing LSR, but initiating LSR can only
continue to discover and exercise specific path of ECMP
if ELI/EL pushing LSR responds with both labels and
associated EL corresponding to label. This is because:
<list style="symbols">
<t>ELI/EL pushing LSR that is a stitching point will
load balance based on EL from previous LSP and pushes
new EL.</t>
<t>Downstream LSR(s) of ELI/EL pushing LSR may load
balance based on new ELs.</t>
</list>
</t>
</list>
The above scenarios point to how the existing multipath
information is insufficient when LSP traceroute is operated on
an LSP with Entropy Labels described by <xref target="RFC6790"
/>. Therefore, this document defines a multipath information
type to be used in the DSMAP/DDMAP of MPLS echo request/reply
packets in <xref target="MPT10" />.
</t>
<t>In addition, responder LSR can reply with empty multipath
information if no IP address set or label set from received
multipath information matched load balancing to a
downstream. Empty return is also possible if initiating LSR sends
multipath information of one type, IP address or label, but
responder LSR load balances on the other type. To disambiguate
between the two results, this document introduces new flags in
the DSMAP/DDMAP TLV to allow responder LSR to describe the load
balance technique being used.</t>
<t>It is required that all LSRs along the LSP understand new
flags as well as new multipath information type. It is also
required that initiating LSR can select both IP destination
address and label to use on transmitting MPLS echo request
packets. Two additional DS Flags are defined for the DSMAP and
DDMAP TLVs in <xref target="DS_Flags" />. These two flags are used by the responder LSR to describe its load balance behavior on received MPLS echo request.</t>
<t>Note that the terms "IP Based Load Balancer", "Label Based Load Balancer" and "Label Based Load Balancer" are in context of how received MPLS echo request is handled by the responder LSR.</t>
</section>
<section title="Multipath Type 9" anchor="MPT9-Sec">
<t>
This section defines to which labels multipath type {9}
applies.
</t>
<t>
<xref target="RFC4379" /> defined multipath type {9} for
tracing of LSPs where label based load-balancing is used.
However, as pointed out in <xref target="RFC6790" />, the
procedures for using this type are incomplete as the specific
location of the label was not defined. It was assumed that
the presence of multipath type {9} implied the value of the
bottom-of-stack label should be varied by the values indicated
by multipath to determine their respective out-going
interfaces.
</t>
<t>
<xref target="EL_FEC" /> defines a new FEC-Stack sub-TLV to
indicate an entropy label. These labels may appear anywhere in
a label stack.
</t>
<t>
Multipath type {9} applies to the first label in the
label-stack that corresponds to an EL-FEC. If no such label
is found, it applies to the label at the bottom of the label
stack.
</t>
</section>
<section title="Pseudowire Tracing">
<t>
This section defines procedures for tracing pseudowires.
These procedures pertain to the use of multipath information
type {9} as well as type {10}. In all cases below, when a
control word is in use the N-flag in the DDMAP or DSMAP MUST
be set. Note that when a control word is not in use the
returned DDMAPs or DSMAPs may not be accurate.
</t>
<t>
In order to trace a non Flow-Aware Pseudowire the initiator
includes an EL-FEC instead of the appropriate PW-FEC at the
bottom of the FEC-Stack. Tracing in this way will cause
compliant routers to return the proper outgoing interface.
Note that this procedure only traces to the end of the MPLS
LSP that is under test and will not verify the PW FEC. To
actually verify the PW-FEC or in the case of a MS-PW, to
determine the next pseudowire label value, the initiator MUST
repeat that step of the trace, (i.e., repeating the TTL value
used) but with the FEC-Stack modified to contain the
appropriate PW-FEC. Note that these procedures are applicable to scenarios which an initiator is able to vary the bottom label (i.e. pseudowire label). Possible scenarios are tracing multiple non Flow-Aware Pseudowires on the same endpoints or tracing a non Flow-Aware Pseudowire provisioned with multiple pseudowire labels.
</t>
<t>In order to trace a Flow Aware Pseudowire, the initiator
includes an EL-FEC at the bottom of the FEC-Stack and pushes
the appropriate PW-FEC onto the FEC-Stack.
</t>
<t>
In order to trace through non-compliant routers the initiator
forms an MPLS echo request message and includes a DDMAP or
DSMAP with multipath type {9}. For a non Flow-Aware Pseudowire
it includes the appropriate PW-FEC in the FEC-Stack. For a
Flow Aware Pseudowire, the initiator includes a NIL-FEC at the
bottom of the FEC-Stack and pushes the appropriate PW-FEC onto
the FEC-Stack.
</t>
<!-- discuss optimization for non Flow Aware -->
<!-- In last procedure if a node processes EL but does not comply with
this draft results may not be accurate. -->
</section>
<section title="Initiating LSR Procedures">
<t>In order to facilitate the flow of the following text we
speak in terms of a boolean called EL_LSP maintained by the
initiating LSR. This value controls the multipath information type to be
used in transmitted echo request packets. When the initiating LSR is
transmitting an echo request packet with DSMAP/DDMAP with a non-zero
multipath information type, then EL_LSP boolean MUST be consulted to
determine the multipath information type to use.
</t>
<t>In addition to procedures described in <xref target="RFC4379"
/> as updated by <xref target="MPT9-Sec" /> and <xref target="RFC6424" />, initiating LSR MUST operate
with following procedures.
<list style="symbols">
<t>When the initiating LSR pushes ELI/EL, initialize EL_LSP=True. Else set EL_LSP=False.</t>
<t>When the initiating LSR is transmitting non-zero multipath
information type:
<list>
<t>If (EL_LSP), the initiating LSR MUST use multipath
information type {10} unless same responder LSR cannot handle type {10}.</t>
<t>Else the initiating LSR MAY use multipath
information type {2, 4, 8, 9}.</t>
</list>
</t>
<t>When the initiating LSR is transmitting multipath information
type {10}, both "IP Multipath Information" and
"Label Multipath Information" MUST be included,
and "IP Associated Label Multipath Information"
MUST be omitted (NULL).</t>
<t>When the initiating LSR receives echo reply with {L=0, E=1} in
DS flags with valid contents, set EL_LSP=True.</t>
</list>
</t>
<t>In following conditions, the initiating LSR may have lost the
ability to exercise specific ECMP paths. The initiating LSR MAY
continue with "best effort".
<list style="symbols">
<t>Received echo reply contains empty multipath
information.</t>
<t>Received echo reply contains {L=0, E=<any>} DS
flags, but does not contain IP multipath information.</t>
<t>Received echo reply contains {L=1, E=<any>} DS
flags, but does not contain label multipath information.</t>
<t>Received echo reply contains {L=<any>, E=1} DS
flags, but does not contain associated label multipath
information.</t>
<t>IP multipath information types {2, 4, 8} sent, and
received echo reply with {L=1, E=0} in DS flags.</t>
<t>Multipath information type {10} sent, and received echo
reply with multipath information type other than {10}.</t>
</list>
</t>
</section>
<section title="Responder LSR Procedures" anchor="Res_LSR_Proc">
<t>Common Procedures: The responder LSR receiving an MPLS echo request
packet with multipath information type {10} MUST validate
following contents. Any deviation MUST result in the responder LSR
to consider the packet as malformed and return code 1
(Malformed echo request received) in the MPLS echo reply packet.
<list style="symbols">
<t>IP multipath information MUST be included.</t>
<t>Label multipath information MUST be included.</t>
<t>IP associated label multipath information MUST be omitted (NULL).</t>
</list>
Following subsections describe expected responder LSR
procedures when echo reply is to include DSMAP/DDMAP TLVs,
based on local load balance technique being employed. In case
the responder LSR performs deviating load balance techniques per
downstream basis, appropriate procedures matching to each
downstream load balance technique MUST be operated.
</t>
<section title="IP Based Load Balancer & Not Pushing ELI/EL">
<t>
<list style="symbols">
<t>The responder MUST set {L=0, E=0} in DS flags.</t>
<t>If multipath information type {2, 4, 8} is received,
the responder MUST comply with <xref target="RFC4379"
/> and <xref target="RFC6424" />.</t>
<t>If multipath information type {9} is received,
the responder MUST reply with multipath type {0}.</t>
<t>If multipath information type {10} is received, following procedures are to be used:
<list style="symbols">
<t>The responder MUST reply with multipath information type {10}.</t>
<t>"Label Multipath Information" and "Associated Label Multipath Information" sections MUST be omitted (NULL).</t>
<t>If no matching IP address is found, then "IPMultipathType" field MUST be set to multipath information type {0} and "IP Multipath Information" section MUST also be omitted (NULL).</t>
<t>If at least one matching IP address is found, then "IPMultipathType" field MUST be set to appropriate multipath information type {2, 4, 8} and "IP Multipath Information" section MUST be included.</t>
</list>
</t>
</list>
</t>
</section>
<section title="IP Based Load Balancer & Pushes ELI/EL">
<t>
<list style="symbols">
<t>The responder MUST set {L=0, E=1} in DS flags.</t>
<t>If multipath information type {9} is received,
the responder MUST reply with multipath type {0}.
</t>
<t>If multipath type {2, 4, 8, 10} is received, following procedures are to be used:
<list style="symbols">
<t>The responder MUST respond with multipath type {10}. See <xref target="MPT10" /> for details of multipath type {10}.</t>
<t>"Label Multipath Information" section MUST be omitted (i.e. is it not there).</t>
<t>IP address set specified in received IP multipath information MUST be used to determine the returning IP/Label pairs.</t>
<t>If received multipath information type was {10}, received "Label Multipath Information" sections MUST NOT be used to determine the associated label portion of returning IP/Label pairs.</t>
<t>If no matching IP address is found, then "IPMultipathType" field MUST be set to multipath information type {0} and "IP Multipath Information" section MUST be omitted. In addition, "Assoc Label Multipath Length" MUST be set to 0, and "Associated Label Multipath Information" section MUST also be omitted.</t>
<t>If at least one matching IP address is found, then "IPMultipathType" field MUST be set to appropriate multipath information type {2, 4, 8} and "IP Multipath Information" section MUST be included. In addition, "Associated Label Multipath Information" section MUST be populated with list of labels corresponding to each IP address specified in "IP Multipath Information" section. "Assoc Label Multipath Length" MUST be set to a value representing length in octets of "Associated Label Multipath Information" field.</t>
</list>
</t>
</list>
</t>
</section>
<section title="Label Based Load Balancer & Not Pushing ELI/EL" anchor="ResLSR_Label_No_ELI">
<t>
<list style="symbols">
<t>The responder MUST set {L=1, E=0} in DS flags.</t>
<t>If multipath information type {2, 4, 8} is received,
the responder MUST reply with multipath type {0}.</t>
<t>If multipath information type {9} is received,
the responder MUST comply with <xref target="RFC4379" />
and <xref target="RFC6424" /> as updated by
<xref target="MPT9-Sec" />.
</t>
<t>If multipath information type {10} is received, following procedures are to be used:
<list style="symbols">
<t>The responder MUST reply with multipath information type {10}.</t>
<t>"IP Multipath Information" and "Associated Label Multipath Information" sections MUST be omitted (NULL).</t>
<t>If no matching label is found, then "LbMultipathType" field MUST be set to multipath information type {0} and "Label Multipath Information" section MUST also be omitted (NULL).</t>
<t>If at least one matching label is found, then "LbMultipathType" field MUST be set to appropriate multipath information type {9} and "Label Multipath Information" section MUST be included.</t>
</list>
</t>
</list>
</t>
</section>
<section title="Label Based Load Balancer & Pushes ELI/EL" anchor="ResLSR_Label_ELI">
<t>
<list style="symbols">
<t>The responder MUST set {L=1, E=1} in DS flags.</t>
<t>If multipath information type {2, 4, 8} is received,
the responder MUST reply with multipath type {0}.</t>
<t>If multipath type {9, 10} is received, following procedures are to be used:
<list style="symbols">
<t>The responder MUST respond with multipath type {10}.</t>
<t>"IP Multipath Information" section MUST be omitted.</t>
<t>Label set specified in received label multipath information MUST be used to determine the returning Label/Label pairs.</t>
<t>If received multipath information type was {10}, received "Label Multipath Information" sections MUST NOT be used to determine the associated label portion of returning Label/Label pairs.</t>
<t>If no matching label is found, then "LbMultipathType" field MUST be set to multipath information type {0} and "Label Multipath Information" section MUST be omitted. In addition, "Assoc Label Multipath Length" MUST be set to 0, and "Associated Label Multipath Information" section MUST also be omitted.</t>
<t>If at least one matching label is found, then "LbMultipathType" field MUST be set to appropriate multipath information type {9} and "Label Multipath Information" section MUST be included. In addition, "Associated Label Multipath Information" section MUST be populated with list of labels corresponding to each label specified in "Label Multipath Information" section. "Assoc Label Multipath Length" MUST be set to a value representing length in octets of "Associated Label Multipath Information" field.</t>
</list>
</t>
</list>
</t>
</section>
<section title="Flow Aware MS-PW Stitching LSR">
<t>Stitching LSR that cross-connects Flow Aware
Pseudowires behave in one of two ways:
<list style="symbols">
<t>Load balances on previous Flow Label, and carries over
same Flow Label. For this case, stitching LSR is to behave as
procedures described in <xref target="ResLSR_Label_No_ELI" />.</t>
<t>Load balances on previous Flow Label, and replaces Flow Label
with newly computed. For this case, stitching LSR is to behave
as procedures described in <xref target="ResLSR_Label_ELI" />.</t>
</list>
</t>
</section>
</section>
<section anchor="EL_FEC" title="Entropy Label FEC">
<t>Entropy Label Indicator (ELI) is a reserved label that has no
explicit FEC associated, and has label value 7 assigned from
the reserved range. Use Nil FEC as Target FEC Stack sub-TLV to
account for ELI in a Target FEC Stack TLV.</t>
<t>Entropy Label (EL) is a special purpose label with label
value being discretionary (i.e. label value may not be from
the reserved range). For LSP verification mechanics to perform
its purpose, it is necessary for a Target FEC Stack sub-TLV to
clearly describe EL, particularly in the scenario where label
stack does not carry ELI (ex: Flow Aware Pseudowire <xref target="RFC6391"
/>). Therefore, this document defines a EL FEC to allow a
Target FEC Stack sub-TLV to be added to the Target FEC Stack
to account for EL.</t>
<t>The Length is 4. Labels are 20-bit values treated as numbers.
<figure align="left"><preamble></preamble><artwork align="left">
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Entropy Label FEC
</artwork></figure>
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 title="DS Flags: L and E" anchor="DS_Flags">
<t>Two flags, L and E, are added in DS Flags field of the
DSMAP/DDMAP TLVs. Both flags MUST NOT be set in echo request
packets when sending, and ignored when received. Zero, one or
both new flags MUST be set in echo reply packets.
<figure align="left"><preamble></preamble><artwork align="left">
DS Flags
--------
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |L|E|I|N|
+-+-+-+-+-+-+-+-+
</artwork></figure>
<figure align="left"><preamble></preamble><artwork align="left">
Flag Name and Meaning
---- ----------------
L Label based load balance indicator
This flag MUST be set to zero in the echo request. LSR
which performs load balancing on a label MUST set this
flag in the echo reply. LSR which performs load
balancing on IP MUST NOT set this flag in the echo
reply.
E ELI/EL push indicator
This flag MUST be set to zero in the echo request. LSR
which pushes ELI/EL MUST set this flag in the echo
reply. LSR which does not push ELI/EL MUST NOT set
this flag in the echo reply.
</artwork></figure>
Two flags result in four load balancing techniques which echo
reply generating LSR can indicate:
<list style="symbols">
<t>{L=0, E=0} LSR load balances based on IP and does not
push ELI/EL.</t>
<t>{L=0, E=1} LSR load balances based on IP and pushes
ELI/EL.</t>
<t>{L=1, E=0} LSR load balances based on label and does not
push ELI/EL.</t>
<t>{L=1, E=1} LSR load balances based on label and pushes
ELI/EL.</t>
</list>
</t>
</section>
<section title="New Multipath Information Type: 10" anchor="MPT10">
<t>One new multipath information type is added to be used in
DSMAP/DDMAP TLVs. New multipath type has value of 10.
<figure align="left"><preamble></preamble><artwork align="left">
Key Type Multipath Information
--- ---------------- ---------------------
10 IP and label set IP addresses and label prefixes
</artwork></figure>
</t>
<t>Multipath type 10 is comprised of three sections. One section
to describe IP address set. One section to describe label
set. One section to describe another label set which associates
to either IP address set or label set specified in the other
section.</t>
<t>Multipath information type 10 has following format:
<figure align="left"><preamble></preamble><artwork align="left">
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IPMultipathType| Reserved(MBZ) | IP Multipath Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| (IP Multipath Information) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|LbMultipathType| Reserved(MBZ) | Label Multipath Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| (Label Multipath Information) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved(MBZ) | Assoc Label Multipath Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| (Associated Label Multipath Information) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Multipath Information Type 10
</artwork></figure>
<list style="symbols">
<t>IPMultipathType
<list>
<t>0 when "IP Multipath Information" is omitted.
Otherwise one of IP multipath information values:
{2, 4, 8}.</t>
</list>
</t>
<t>IP Multipath Information
<list>
<t>This section is omitted when "IPMultipathType"
is 0. Otherwise this section reuses IP multipath information
from <xref target="RFC4379" />. Specifically, multipath
information for values {2, 4, 8} can be used.</t>
</list>
</t>
<t>LbMultipathType
<list>
<t>0 when "Label Multipath Information" is omitted.
Otherwise label multipath information value {9}.</t>
</list>
</t>
<t>Label Multipath Information
<list>
<t>This section is omitted when "LbMultipathType"
is 0. Otherwise this section reuses label multipath
information from <xref target="RFC4379" />. Specifically,
multipath information for value {9} can be used.</t>
</list>
</t>
<t>Associated Label Multipath Information
<list>
<t>"Assoc Label Multipath Length" is a 16 bit field of multipath information which indicates length in octets of the associated label multipath information.</t>
<t>"Associated Label Multipath Information" is a list of labels with each label described in 24 bits. This section MUST be omitted in an MPLS echo request message. A midpoint which pushes ELI/EL labels SHOULD include "Assoc Label Multipath Information" in its MPLS echo reply message, along with either "IP Multipath Information" or "Label Multipath Information". Each specified associated label described in this section maps to specific IP address OR label described in the "IP Multipath Information" section or "Label Multipath Information" section. For example, if 3 IP addresses are specified in the "IP Multipath Information" section, then there MUST be 3 labels described in this section. First label maps to the lowest IP address specified, second label maps to the second lowest IP address specified and third label maps to the third lowest IP address specified.</t>
</list>
</t>
</list>
</t>
</section>
<section title="Supported and Unsupported Cases" anchor="_CASES">
<?rfc subcompact="yes" ?>
<t>MPLS architecture never defined strict rules on how implementations are to identify hash "keys" for load balancing purpose. As result, implementations may be of following load balancer types:
<list style="numbers">
<t>IP Based Load Balancer.</t>
<t>Label Based Load Balancer.</t>
<t>Label and IP Based Load Balancer.</t>
</list>
For cases (2) and (3), implementation can include different sets of labels from the label stack for load balancing purpose. Thus following sub-cases are possible:
<list style="letters">
<t>Entire label stack.</t>
<t>Top N labels from label stack where number of labels in label stack is >N.</t>
<t>Bottom N labels from label stack where number of labels in label stack is >N.</t>
</list>
In a scenario where there is one Flow Label or Entropy Label present in the label stack, following further cases are possible for (2b), (2c), (3b) and (3c):
<list style="numbers">
<t>N labels from label stack include Flow Label or Entropy Label.</t>
<t>N labels from label stack does not include Flow Label or Entropy Label.</t>
</list>
Also in a scenario where there are multiple Entropy Labels present in the label stack, it is possible for implementations to employ deviating techniques:
<list style="symbols">
<t>Search for entropy stops at the first Entropy Label.</t>
<t>Search for entropy includes any Entropy Label found plus continues to search for entropy in the label stack.</t>
</list>
Furthermore, handling of reserved (i.e. special) labels varies among implementations:
<list style="symbols">
<t>Reserved labels are used in the hash as any other label would be (a bad practice).</t>
<t>Reserved labels are skipped over and, for implementations limited to N labels, the reserved labels do not count towards the limit of N.</t>
<t>Reserved labels are skipped over and, for implementations limited to N labels, the reserved labels count towards the limit of N.</t>
</list>
It is important to point this out since presence of GAL will affect those implementations which include reserved labels for load balancing purpose.</t>
<t>As can be seen from above, there are many flavors of potential load balancing implementations. Attempting for any OAM tools to support ECMP discovery and traversal over all flavors of such will require fairly complex procedures and implementations to support those complex procedures. Complexities in OAM tools will produce minimal benefits if majority of implementations are expected to employ small subset of cases described above.
<?rfc subcompact="no" ?>
<list style="symbols">
<t>Section 4.3 of <xref target="RFC6790" /> states that implementations, for load balancing purpose, parsing beyond the label stack after finding Entropy Label is "limited incremental value". Therefore, it is expected that most implementations will be of types "IP Based Load Balancer" or "Label Based Load Balancer".</t>
<t>Section 2.4.5.1 of <xref target="I-D.ietf-mpls-forwarding" /> recommends that search for entropies from the label stack should terminate upon finding the first Entropy Label. Therefore, it is expected that implementations will only include the first (top-most) Entropy Label when there are multiple Entropy Labels in the label stack.</t>
<t>It is expected that, in most cases, number of labels in the label stack will not exceed number of labels (N) which implementations can include for load balancing purpose.</t>
<t>It is expected that labels in the label stack, besides Flow Label and Entropy Label, are constant for the lifetime of a single LSP multipath traceroute operation. Therefore, deviating load balancing implementations with respect to reserved labels should not affect this tool.</t>
</list>
Thus <xref target="RFC4379" />, <xref target="RFC6424" /> and this document will support cases (1) and (2a1), where only the first (top-most) Entropy Label is included when there are multiple Entropy Labels in the label stack.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>This document extends LSP Traceroute mechanism to discover
and exercise ECMP paths when LSP uses ELI/EL in label stack.
Additional processings are required for responder and initiator
nodes. Responder node that pushes ELI/EL will need to compute
and return multipath data including associated EL. Initiator
node will need to store and handle both IP multipath and label
multipath information, and include destination IP addresses
and/or ELs in MPLS echo request packet as well as in carried
multipath information to downstream nodes. Due to additional
processing, it is critical that proper security measures
described in <xref target="RFC4379" /> and
<xref target="RFC6424" /> are followed.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<section title="DS Flags">
<t>The IANA is requested to assign new bit numbers from the "DS flags" sub-registry from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry (<xref target="IANA-MPLS-LSP-PING" />).</t>
<t>Note: the "DS flags" sub-registry is created by <xref target="I-D.decraene-mpls-lsp-ping-registry" />.
<figure align="left"><preamble></preamble><artwork align="left">
Bit number Name Reference
---------- ---------------------------------------- ---------
TBD2(5) E: ELI/EL push indicator this document
TBD3(4) L: Label based load balance indicator this document
</artwork></figure>
This document requests the bit number 5 as TBD2, and the bit number 4 as TBD3.
</t>
</section>
<section title="Multpath Type">
<t>The IANA is requested to assign a new value from the "Multipath Type" sub-registry from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry (<xref target="IANA-MPLS-LSP-PING" />).</t>
<t>Note: the "Multipath Type" sub-registry is created by <xref target="I-D.decraene-mpls-lsp-ping-registry" />.
<figure align="left"><preamble></preamble><artwork align="left">
Value Meaning Reference
---------- ---------------------------------------- ---------
TBD4(10) IP and label set this document
</artwork></figure>
This document requests the value 10 as TBD4.
</t>
</section>
<section title="Entropy Label FEC">
<t>The IANA is requested to assign a new sub-TLV from the "Sub-TLVs for TLV Types 1 and 16" section from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry (<xref target="IANA-MPLS-LSP-PING" />).
<figure align="left"><preamble></preamble><artwork align="left">
Sub-Type Sub-TLV Name Reference
-------- ------------ ---------
TBD1 Entropy Label FEC this document
</artwork></figure>
</t>
</section>
</section>
<section title="Acknowledgements">
<t>Authors would like to thank Loa Andersson, Curtis Villamizar, Daniel King and Sriganesh Kini for performing thorough review and providing valuable comments.</t>
</section>
<section title="Contributing Authors">
<t>Nagendra Kumar
<vspace blankLines="0" />
Cisco Systems
<vspace blankLines="0" />
Email: naikumar@cisco.com</t>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<!-- References split into informative and normative -->
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.4379"?>
<?rfc include="reference.RFC.6790"?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.6424"?>
<?rfc include="reference.RFC.6391"?>
<?rfc include="reference.I-D.ietf-mpls-forwarding"?>
<?rfc include="reference.I-D.ravisingh-mpls-el-for-seamless-mpls"?>
<?rfc include="reference.I-D.decraene-mpls-lsp-ping-registry"?>
<reference anchor="IANA-MPLS-LSP-PING" target="http://www.iana.org/assignments/mpls-lsp-ping-parameters/mpls-lsp-ping-parameters.xhtml">
<front>
<title>Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters</title>
<author><organization>IANA</organization></author>
<date/>
</front>
</reference>
</references>
<!-- Change Log
v00-a 2013-05-29 Nobo: Initial version
v02-a 2014-01-25 Nobo: Addressed MPLS-RT review comments
-->
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 05:30:28 |