Label Switched Path (LSP) Ping/Trace Multipath Support for Link Aggregation Group (LAG) Interfaces
draft-ietf-mpls-lsp-ping-lag-multipath-05
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8611.
|
|
|---|---|---|---|
| Authors | Nobo Akiya , George Swallow , Stephane Litkowski , Bruno Decraene , John Drake , Mach Chen | ||
| Last updated | 2018-12-13 (Latest revision 2018-10-23) | ||
| Replaces | draft-akiya-mpls-lsp-ping-lag-multipath | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
TSVART Last Call review
by Joerg Ott
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Associated WG milestone |
|
||
| Document shepherd | Loa Andersson | ||
| Shepherd write-up | Show Last changed 2018-08-03 | ||
| IESG | IESG state | Became RFC 8611 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Deborah Brungard | ||
| Send notices to | (None) | ||
| IANA | IANA review state | IANA OK - Actions Needed |
draft-ietf-mpls-lsp-ping-lag-multipath-05
Internet Engineering Task Force N. Akiya
Internet-Draft Big Switch Networks
Updates: 8029 (if approved) G. Swallow
Intended status: Standards Track Cisco Systems
Expires: April 26, 2019 S. Litkowski
B. Decraene
Orange
J. Drake
Juniper Networks
M. Chen
Huawei
October 23, 2018
Label Switched Path (LSP) Ping/Trace Multipath Support for
Link Aggregation Group (LAG) Interfaces
draft-ietf-mpls-lsp-ping-lag-multipath-05
Abstract
This document defines extensions to the MPLS Label Switched Path
(LSP) Ping and Traceroute mechanisms as specified in RFC 8029. The
extensions allow the MPLS LSP Ping and Traceroute mechanisms to
discover and exercise specific paths of Layer 2 (L2) Equal-Cost
Multipath (ECMP) over Link Aggregation Group (LAG) interfaces.
Additionally, a mechanism is defined to enable determination of the
capabilities of an LSR supported.
This document updates RFC8029.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 26, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Background . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of Solution . . . . . . . . . . . . . . . . . . . . 4
3. LSR Capability Discovery . . . . . . . . . . . . . . . . . . 6
3.1. Initiator LSR Procedures . . . . . . . . . . . . . . . . 7
3.2. Responder LSR Procedures . . . . . . . . . . . . . . . . 7
4. Mechanism to Discover L2 ECMP Multipath . . . . . . . . . . . 7
4.1. Initiator LSR Procedures . . . . . . . . . . . . . . . . 7
4.2. Responder LSR Procedures . . . . . . . . . . . . . . . . 8
4.3. Additional Initiator LSR Procedures . . . . . . . . . . . 10
5. Mechanism to Validate L2 ECMP Traversal . . . . . . . . . . . 11
5.1. Incoming LAG Member Links Verification . . . . . . . . . 11
5.1.1. Initiator LSR Procedures . . . . . . . . . . . . . . 11
5.1.2. Responder LSR Procedures . . . . . . . . . . . . . . 12
5.1.3. Additional Initiator LSR Procedures . . . . . . . . . 12
5.2. Individual End-to-End Path Verification . . . . . . . . . 13
6. LSR Capability TLV . . . . . . . . . . . . . . . . . . . . . 14
7. LAG Description Indicator Flag: G . . . . . . . . . . . . . . 15
8. Local Interface Index Sub-TLV . . . . . . . . . . . . . . . . 16
9. Remote Interface Index Sub-TLV . . . . . . . . . . . . . . . 17
10. Detailed Interface and Label Stack TLV . . . . . . . . . . . 17
10.1. Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1.1. Incoming Label Stack Sub-TLV . . . . . . . . . . . . 19
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10.1.2. Incoming Interface Index Sub-TLV . . . . . . . . . . 20
11. Security Considerations . . . . . . . . . . . . . . . . . . . 21
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
12.1. LSR Capability TLV . . . . . . . . . . . . . . . . . . . 21
12.1.1. LSR Capability Flags . . . . . . . . . . . . . . . . 21
12.2. Local Interface Index Sub-TLV . . . . . . . . . . . . . 22
12.2.1. Interface Index Flags . . . . . . . . . . . . . . . 22
12.3. Remote Interface Index Sub-TLV . . . . . . . . . . . . . 22
12.4. Detailed Interface and Label Stack TLV . . . . . . . . . 23
12.4.1. Sub-TLVs for TLV Type TBD4 . . . . . . . . . . . . . 23
12.5. DS Flags . . . . . . . . . . . . . . . . . . . . . . . . 23
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
14.1. Normative References . . . . . . . . . . . . . . . . . . 24
14.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. LAG with intermediate L2 Switch Issues . . . . . . . 25
A.1. Equal Numbers of LAG Members . . . . . . . . . . . . . . 25
A.2. Deviating Numbers of LAG Members . . . . . . . . . . . . 25
A.3. LAG Only on Right . . . . . . . . . . . . . . . . . . . . 26
A.4. LAG Only on Left . . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
1.1. Terminology
The following acronyms/terms are used in this document:
o MPLS - Multiprotocol Label Switching.
o LSP - Label Switched Path.
o LSR - Label Switching Router.
o ECMP - Equal-Cost Multipath.
o LAG - Link Aggregation Group.
o Initiator LSR - LSR which sends MPLS echo request.
o Responder LSR - LSR which receives MPLS echo request and sends
MPLS echo reply.
1.2. Background
The MPLS Label Switched Path (LSP) Ping and Traceroute mechanisms
[RFC8029] are powerful tools designed to diagnose all available Layer
3 (L3) paths of LSPs, including diagnostic coverage of L3 Equal-Cost
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Multipath (ECMP). In many MPLS networks, Link Aggregation Group
(LAG) as defined in [IEEE802.1AX], which provides Layer 2 (L2) ECMP,
is often used for various reasons. MPLS LSP Ping and Traceroute
tools were not designed to discover and exercise specific paths of L2
ECMP. This raises a limitation for the following scenario when an
LSP traverses over a LAG:
o Label switching over some member links of the LAG is successful,
but will be failed over other member links of the LAG.
o MPLS echo request for the LSP over the LAG is load balanced on one
of the member links which is label switching successfully.
With the above scenarios, MPLS LSP Ping and Traceroute will not be
able to detect the label switching failure of the problematic member
link(s) of the LAG. In other words, lack of L2 ECMP diagnostic
coverage can produce an outcome where MPLS LSP Ping and Traceroute
can be blind to label switching failures over a problematic LAG
interface. It is, thus, desirable to extend the MPLS LSP Ping and
Traceroute to have deterministic diagnostic coverage of LAG
interfaces.
The need for a solution of this problem was motivated by issues
encountered in live networks.
2. Overview of Solution
This document defines an optional TLV to discover the capabilities of
a responder LSR and extensions for use with the MPLS LSP Ping and
Traceroute mechanisms to describe Multipath Information for
individual LAG member links, thus allowing MPLS LSP Ping and
Traceroute to discover and exercise specific paths of L2 ECMP over
LAG interfaces. The reader is expected to be familiar with mechanics
of Downstream Mapping described in Section 3.3 of [RFC8029] and
Downstream Detailed Mapping TLV (DDMAP) described in Section 3.4 of
[RFC8029].
The solution consists of the MPLS echo request containing a DDMAP TLV
and the optional LSR capability TLV to indicate that separate load
balancing information for each L2 nexthop over LAG is desired in the
MPLS echo reply. The Responder LSR places the same optional LSR
capability TLV in the MPLS echo reply to provide acknowledgement back
to the initiator LSR. It also adds, for each downstream LAG member,
load balance information (i.e., multipath information and interface
index). This mechanism is applicable to all types of LSPs which can
traverse over LAG interfaces. Many LAGs are built from p2p links,
with router X and router X+1 having direct connectivity and the same
number of LAG members. It is possible to build LAGs asymmetrically
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by using Ethernet switches between two routers. Appendix A lists
some use cases for which the mechanisms defined in this document may
not be applicable. Note that the mechanisms described in this
document do not impose any changes to scenarios where an LSP is
pinned down to a particular LAG member (i.e. the LAG is not treated
as one logical interface by the LSP).
The following figure and description provides an example using an LDP
network.
<----- LDP Network ----->
+-------+
| |
A-------B=======C-------E
| |
+-------D-------+
---- Non-LAG
==== LAG comprising of two member links
Figure 1: Example LDP Network
When node A is initiating LSP Traceroute to node E, node B will
return to node A load balance information for following entries.
1. Downstream C over Non-LAG (upper path).
2. First Downstream C over LAG (middle path).
3. Second Downstream C over LAG (middle path).
4. Downstream D over Non-LAG (lower path).
This document defines:
o In Section 3, a mechanism to discover capabilities of responder
LSRs;
o In Section 4, a mechanism to discover L2 ECMP multipath
information;
o In Section 5, a mechanism to validate L2 ECMP traversal;
o In Section 6, the LSR Capability TLV;
o In Section 7, the LAG Description Indicator flag;
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o In Section 8, the Local Interface Index Sub-TLV;
o In Section 9, the Remote Interface Index Sub-TLV;
o In Section 10, the Detailed Interface and Label Stack TLV;
3. LSR Capability Discovery
The MPLS Ping operates by an initiator LSR sending an MPLS echo
request message and receiving back a corresponding MPLS echo reply
message from a responder LSR. The MPLS Traceroute operates in a
similar way except the initiator LSR potentially sends multiple MPLS
echo request messages with incrementing TTL values.
There have been many extensions to the MPLS Ping and Traceroute
mechanism over the years. Thus it is often useful, and sometimes
necessary, for the initiator LSR to deterministically disambiguate
the differences between:
o The responder LSR sent the MPLS echo reply message with contents C
because it has feature X, Y and Z implemented.
o The responder LSR sent the MPLS echo reply message with contents C
because it has subset of features X, Y and Z implemented but not
all.
o The responder LSR sent the MPLS echo reply message with contents C
because it does not have features X, Y and Z implemented.
To allow the initiator LSR to disambiguate the above differences,
this document defines the LSR Capability TLV (described in
Section 6). When the initiator LSR wishes to discover the
capabilities of the responder LSR, the initiator LSR includes the LSR
Capability TLV in the MPLS echo request message. When the responder
LSR receives an MPLS echo request message with the LSR Capability TLV
included, if it knows the LSR Capability TLV, then it MUST include
the LSR Capability TLV in the MPLS echo reply message with the LSR
Capability TLV describing features and extensions supported by the
local LSR. Otherwise, an MPLS echo reply MUST be sent back to the
initiator LSR with the return code set to "One or more of the TLVs
was not understood". Then the initiator LSR can send another MPLS
echo request without including the LSR Capability TLV.
It is RECOMMENDED that implementations supporting the LAG Multipath
extensions defined in this document include the LSR Capability TLV in
MPLS echo request messages.
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3.1. Initiator LSR Procedures
If an initiator LSR does not know what capabilities a responder LSR
can support, it can send an MPLS each request message and carry the
LSR Capability TLV to the responder to discover the capabilities that
the responder LSR can support.
3.2. Responder LSR Procedures
When a responder LSR received an MPLS echo request message that
carries the LSR Capability TLV, the following procedures are used:
If the responder knows how to process the LSR Capability TLV, the
following procedures are used:
o The responder LSR MUST include the LSR Capability TLV in the MPLS
echo reply message.
o If the responder LSR understands the "LAG Description Indicator
flag":
* Set the "Downstream LAG Info Accommodation flag" if the
responder LSR is capable of describing outgoing LAG member
links separately; otherwise, clear the "Downstream LAG Info
Accommodation flag".
* Set the "Upstream LAG Info Accommodation flag" if responder LSR
is capable of describing incoming LAG member links separately;
otherwise, clear the "Upstream LAG Info Accommodation flag".
o If the responder LSR does not understand the "LAG Description
Indicator flag":
* Clear both the "Downstream LAG Info Accommodation flag" and the
"Upstream LAG Info Accommodation flag".
If the responder does not know the LSR Capability TLV, an MPLS echo
reply with the return code set to "One or more of the TLVs was not
understood" MUST be sent back to the initiator LSR.
4. Mechanism to Discover L2 ECMP Multipath
4.1. Initiator LSR Procedures
Through the "LSR Capability Discovery" as defined in Section 3, the
initiator LSR can understand whether the responder LSR can describe
incoming/outgoing LAG member links separately in the DDMAP TLV.
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Once the initiator LSR knows the capabilities that a responder
supports, then it sends an MPLS echo request carrying a DDMAP with
the "LAG Description Indicator flag" (G) set to the responder LSR.
The "LAG Description Indicator flag" (G) indicates that separate load
balancing information for each L2 nexthop over a LAG is desired in
the MPLS echo reply. The new "LAG Description Indicator flag" is
described in Section 7.
4.2. Responder LSR Procedures
When a responder LSR received an MPLS echo request message with the
"LAG Description Indicator flag" set, if the responder LSR
understands the "LAG Description Indicator flag" and is capable of
describing outgoing LAG member links separately, the following
procedures are used, regardless of whether or not outgoing interfaces
include LAG interfaces:
o For each downstream that is a LAG interface:
* The responder LSR MUST include a DDMAP TLV when sending the
MPLS echo reply.
* The responder LSR MUST set the "LAG Description Indicator flag"
in the DS Flags field of the DDMAP TLV.
* In the DDMAP TLV, the Local Interface Index Sub-TLV, Remote
Interface Index Sub-TLV and Multipath Data Sub-TLV are used to
describe each LAG member link. All other fields of the DDMAP
TLV are used to describe the LAG interface.
* For each LAG member link of the LAG interface:
+ The responder LSR MUST add a Local Interface Index Sub-TLV
(described in Section 8) with the "LAG Member Link Indicator
flag" set in the Interface Index Flags field, describing the
interface index of this outgoing LAG member link (the local
interface index is assigned by the local LSR).
+ The responder LSR MAY add a Remote Interface Index Sub-TLV
(described in Section 9) with the "LAG Member Link Indicator
flag" set in the Interface Index Flags field, describing the
interface index of the incoming LAG member link on the
downstream LSR (this interface index is assigned by the
downstream LSR). How the local LSR obtains the interface
index of the LAG member link on the downstream LSR is
outside the scope of this document.
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+ The responder LSR MUST add an Multipath Data Sub-TLV for
this LAG member link, if the received DDMAP TLV requested
multipath information.
Based on the procedures described above, every LAG member link will
have a Local Interface Index Sub-TLV and a Multipath Data Sub-TLV
entries in the DDMAP TLV. The order of the Sub-TLVs in the DDMAP TLV
for a LAG member link MUST be Local Interface Index Sub-TLV
immediately followed by Multipath Data Sub-TLV. A LAG member link
may also have a corresponding Remote Interface Index Sub-TLV. When a
Local Interface Index Sub-TLV, a Remote Interface Index-Sub-TLV and a
Multipath Data Sub-TLV are placed in the DDMAP TLV to describe a LAG
member link, they MUST be placed in the order of Local Interface
Index Sub-TLV, Remote Interface Index-Sub-TLV and Multipath Data Sub-
TLV.
A responder LSR possessing a LAG interface with two member links
would send the following DDMAP for this LAG interface:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ DDMAP fields describing LAG interface with DS Flags G set ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[MANDATORY] Local Interface Index Sub-TLV of LAG member link #1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[OPTIONAL] Remote Interface Index Sub-TLV of LAG member link #1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[MANDATORY] Multipath Data Sub-TLV LAG member link #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[MANDATORY] Local Interface Index Sub-TLV of LAG member link #2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[OPTIONAL] Remote Interface Index Sub-TLV of LAG member link #2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[MANDATORY] Multipath Data Sub-TLV LAG member link #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Stack Sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Example of DDMAP in MPLS Echo Reply
When none of the received multipath information maps to a particular
LAG member link, then the responder LSR MUST still place the Local
Interface Index Sub-TLV and the Multipath Data Sub-TLV for that LAG
member link in the DDMAP TLV, the value of Multipath Length field of
the Multipath Data Sub-TLV is set to zero.
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4.3. Additional Initiator LSR Procedures
The procedures above allow an initiator LSR to:
o Identify whether or not the responder LSR can describe outgoing
LAG member links separately, by looking at the LSR Capability TLV.
o Utilize the value of the "LAG Description Indicator flag" in DS
Flags to identify whether each received DDMAP TLV describes a LAG
interface or a non-LAG interface.
o Obtain multipath information which is expected to traverse the
specific LAG member link described by corresponding interface
index.
When an initiator LSR receives a DDMAP containing LAG member
information from a downstream LSR with TTL=n, then the subsequent
DDMAP sent by the initiator LSR to the downstream LSR with TTL=n+1
through a particular LAG member link MUST be updated with following
procedures:
o The Local Interface Index Sub-TLVs MUST be removed in the sending
DDMAP.
o If the Remote Interface Index Sub-TLVs were present and the
initiator LSR is traversing over a specific LAG member link, then
the Remote Interface Index Sub-TLV corresponding to the LAG member
link being traversed SHOULD be included in the sending DDMAP. All
other Remote Interface Index Sub-TLVs MUST be removed from the
sending DDMAP.
o The Multipath Data Sub-TLVs MUST be updated to include just one
Multipath Data Sub-TLV. The initiator LSR MAY just keep the
Multipath Data Sub-TLV corresponding to the LAG member link being
traversed, or combine the Multipath Data Sub-TLVs for all LAG
member links into a single Multipath Data Sub-TLV when diagnosing
further downstream LSRs.
o All other fields of the DDMAP are to comply with procedures
described in [RFC8029].
Figure 3 is an example that shows how to use the DDMAP TLV to notify
which member link (link #1 in the example) will be chosen to send the
MPLS echo request message to the next downstream LSR:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ DDMAP fields describing LAG interface with DS Flags G set ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[OPTIONAL] Remote Interface Index Sub-TLV of LAG member link #1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multipath Data Sub-TLV LAG member link #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Stack Sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Example of DDMAP in MPLS Echo Request
5. Mechanism to Validate L2 ECMP Traversal
Section 4 defines the responder LSR procedures to constructs a DDMAP
for a downstream LAG. The Remote Interface Index Sub-TLVs that
describes the incoming LAG member links of the downstream LSR is
optional, because this information from the downstream LSR is often
not available on the responder LSR. In such case, the traversal of
LAG member links can be validated with procedures described in
Section 5.1. If LSRs can provide the Remote Interface Index Sub-
TLVs, then the validation procedures described in Section 5.2 can be
used.
5.1. Incoming LAG Member Links Verification
Without downstream LSRs returning remote Interface Index Sub-TLVs in
the DDMAP, validation of the LAG member link traversal requires that
initiator LSR traverses all available LAG member links and taking the
results through a logic. This section provides the mechanism for the
initiator LSR to obtain additional information from the downstream
LSRs and describes the additional logic in the initiator LSR to
validate the L2 ECMP traversal.
5.1.1. Initiator LSR Procedures
An MPLS echo request carrying a DDMAP TLV with the "Interface and
Label Stack Object Request flag" and "LAG Description Indicator flag"
set is sent to indicate the request for Detailed Interface and Label
Stack TLV with additional LAG member link information (i.e.
interface index) in the MPLS echo reply.
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5.1.2. Responder LSR Procedures
A responder LSR that understands the "LAG Description Indicator flag"
and is capable of describing incoming LAG member link MUST use the
following procedures, regardless of whether or not incoming interface
was a LAG interface:
o When the "I" flag ( "Interface and Label Stack Object Request
flag") of the DDMAP TLV in the received MPLS echo request is set:
* The responder LSR MUST add the Detailed Interface and Label
Stack TLV (described in Section 10) in the MPLS echo reply.
* If the incoming interface is a LAG, the responder LSR MUST add
the Incoming Interface Index Sub-TLV (described in
Section 10.1.2) in the Detailed Interface and Label Stack TLV.
The "LAG Member Link Indicator flag" MUST be set in the
Interface Index Flags field, and the Interface Index field set
to the LAG member link which received the MPLS echo request.
These procedures allow initiator LSR to:
o Utilize the Incoming Interface Index Sub-TLV in the Detailed
Interface and Label Stack TLV to derive, if the incoming interface
is a LAG, the identity of the incoming LAG member.
5.1.3. Additional Initiator LSR Procedures
Along with procedures described in Section 4, the procedures
described in this section will allow an initiator LSR to know:
o The expected load balance information of every LAG member link, at
LSR with TTL=n.
o With specific entropy, the expected interface index of the
outgoing LAG member link at TTL=n.
o With specific entropy, the interface index of the incoming LAG
member link at TTL=n+1.
Expectation is that there's a relationship between the interface
index of the outgoing LAG member link at TTL=n and the interface
index of the incoming LAG member link at TTL=n+1 for all discovered
entropies. In other words, set of entropies that load balances to
outgoing LAG member link X at TTL=n should all reach the nexthop on
same incoming LAG member link Y at TTL=n+1.
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With additional logics, the initiator LSR can perform the following
checks in a scenario where the initiator LSR knows that there is a
LAG, with two LAG members, between TTL=n and TTL=n+1, and has the
multipath information to traverse the two LAG member links.
The initiator LSR sends two MPLS echo request messages to traverse
the two LAG member links at TTL=n+1:
o Success case:
* One MPLS echo request message reaches TTL=n+1 on an LAG member
link 1.
* The other MPLS echo request message reaches TTL=n+1 on an LAG
member link 2.
The two MPLS echo request messages sent by the initiator LSR reach
at the immediate downstream LSR from two different LAG member
links.
o Error case:
* One MPLS echo request message reaches TTL=n+1 on an LAG member
link 1.
* The other MPLS echo request message also reaches TTL=n+1 on an
LAG member link 1.
One or two MPLS echo request messages sent by the initiator LSR
cannot reach the immediate downstream LSR, or the two MPLS echo
request messages reach at the immediate downstream LSR from the
same LAG member link.
Note that the above defined procedures will provide a deterministic
result for LAG interfaces that are back-to-back connected between
LSRs (i.e. no L2 switch in between). If there is a L2 switch between
the LSR at TTL=n and the LSR at TTL=n+1, there is no guarantee that
traversal of every LAG member link at TTL=n will result in reaching
from different interface at TTL=n+1. Issues resulting from LAG with
L2 switch in between are further described in Appendix A. LAG
provisioning models in operated network should be considered when
analyzing the output of LSP Traceroute exercising L2 ECMPs.
5.2. Individual End-to-End Path Verification
When the Remote Interface Index Sub-TLVs are available from an LSR
with TTL=n, then the validation of LAG member link traversal can be
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performed by the downstream LSR of TTL=n+1. The initiator LSR
follows the procedures described in Section 4.3.
The DDMAP validation procedures for the downstream responder LSR are
then updated to include the comparison of the incoming LAG member
link to the interface index described in the Remote Interface Index
Sub-TLV in the DDMAP TLV. Failure of this comparison results in the
return code being set to "Downstream Mapping Mismatch (5)".
6. LSR Capability TLV
This document defines a new optional TLV which is referred to as the
"LSR Capability TLV. It MAY be included in the MPLS echo request
message and the MPLS echo reply message. An MPLS echo request
message and an MPLS echo reply message MUST NOT include more than one
LSR Capability TLV. The presence of an LSR Capability TLV in an MPLS
echo request message is a request that a responder LSR includes an
LSR Capability TLV in the MPLS echo reply message, with the LSR
Capability TLV describing features and extensions that the responder
LSR supports.
When a responder LSR received an MPLS echo request message that
carries an LSR Capability TLV, if the responder LSR knows how to
process the LSR Capability TLV, an LSR Capability TLV MUST be
included in the MPLS echo reply message. Otherwise, if the responder
does not know the LSR Capability TLV, an MPLS echo reply with the
return code set to "One or more of the TLVs was not understood" MUST
be sent back to the initiator LSR.
The format of the LSR Capability TLV is as below:
LSR Capability TLV Type is TBD1. Length is 4. The value field of
the LSR Capability TLV has following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSR Capability Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: LSR Capability TLV
Where:
The Type is 2 octets in length and the value is TBD1.
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The Length filed is 2 octets in length, and the value is 4.
The LSR Capability Flags is 4 octets in length, this document
defines following flags:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero (Reserved) |U|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This document defines two flags. The remaining flags MUST be set
to zero when sending and ignored on receipt. Both the U and the D
flag MUST be cleared in the MPLS echo request message when
sending, and ignored on receipt. Neither, either or both the U
and the D flag MAY be set in the MPLS echo reply message.
Flag Name and Meaning
---- ----------------
U Upstream LAG Info Accommodation
An LSR sets this flag when the LSR is capable of
describing a LAG member link in the Incoming Interface
Index Sub-TLV in the Detailed Interface and
Label Stack TLV.
D Downstream LAG Info Accommodation
An LSR sets this flag when the LSR is capable of
describing LAG member links in the Local Interface
Index Sub-TLV and the Multipath Data Sub-TLV in the
Downstream Detailed Mapping TLV.
7. LAG Description Indicator Flag: G
This document defines a flag, the "G" flag (LAG Description
Indicator), in the DS Flags field of the DDMAP TLV.
The "G" flag in the MPLS echo request message indicates the request
for detailed LAG information from the responder LSR. In the MPLS
echo reply message, the "G" flag MUST be set if the DDMAP TLV
describes a LAG interface. It MUST be cleared otherwise.
The "G" flag is defined as below:
The Bit Number is TBD5.
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0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |G|MBZ|I|N|
+-+-+-+-+-+-+-+-+
RFC-Editor-Note: Please update above figure to place the G flag in
the bit number TBD5.
Flag Name and Meaning
---- ----------------
G LAG Description Indicator
When this flag is set in the MPLS echo request, the responder LSR
is requested to respond with detailed LAG information. When this
flag is set in the MPLS echo reply, the corresponding DDMAP TLV
describes a LAG interface.
8. Local Interface Index Sub-TLV
The Local Interface Index Sub-TLV is an optional TLV, it describes
the interface index assigned by the local LSR to an egress interface.
One or more Local Interface Index sub-TLVs MAY appear in a DDMAP TLV.
The format of the Local Interface Index Sub-TLV is below:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Local Interface Index Sub-TLV
Where:
o The "Type" field is 2 octets in length, the value is TBD2.
o The "Length" filed 2 octets in length, and the value is 4.
o The "Local Interface Index" field is 4 octets in length, it is an
interface index assigned by a local LSR to an egress interface.
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9. Remote Interface Index Sub-TLV
The Remote Interface Index Sub-TLV is an optional TLV, it describes
the interface index assigned by a downstream LSR to an ingress
interface. One or more Remote Interface Index sub-TLVs MAY appear in
a DDMAP TLV.
The format of the Remote Interface Index Sub-TLV is as below:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Remote Interface Index Sub-TLV
Where:
o The "Type" field is 2 octets in length, and the value is TBD3.
o The "Length" field is 2 octets in length, and the value is 4.
o The "Remote Interface Index" is 4 octets in length, it is an
interface index assigned by a downstream LSR to an ingress
interface.
10. Detailed Interface and Label Stack TLV
The "Detailed Interface and Label Stack" object is a TLV that MAY be
included in an MPLS echo reply message to report the interface on
which the MPLS echo request message was received and the label stack
that was on the packet when it was received. A responder LSR MUST
NOT insert more than one instance of this TLV into the MPLS echo
reply message. This TLV allows the initiator LSR to obtain the exact
interface and label stack information as it appears at the responder
LSR.
Detailed Interface and Label Stack TLV Type is TBD4. Length is K +
Sub-TLV Length (sum of Sub-TLVs). K is the sum of all fields of this
TLV prior to Sub-TLVs, but the length of K depends on the Address
Type. Details of this information is described below. The Value
field has following format:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. List of Sub-TLVs .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Detailed Interface and Label Stack TLV
The Detailed Interface and Label Stack TLV format is derived from the
Interface and Label Stack TLV format (from [RFC8029]). Two changes
are introduced. The first is that the label stack is converted into
a sub-TLV. The second is that a new sub-TLV is added to describe an
interface index. These fields of Detailed Interface and Label Stack
TLV have the same use and meaning as in [RFC8029]. A summary of
these fields is as below:
Address Type
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 length of the
initial part of the TLV is listed as "K Octets". The Address
Type is set to one of the following values:
Type # Address Type K Octets
------ ------------ --------
1 IPv4 Numbered 16
2 IPv4 Unnumbered 16
3 IPv6 Numbered 40
4 IPv6 Unnumbered 28
IP Address and Interface
IPv4 addresses and interface indices are encoded in 4 octets;
IPv6 addresses are encoded in 16 octets.
If the interface upon which the echo request message was
received is numbered, then the Address Type MUST be set to IPv4
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Numbered or IPv6 Numbered, 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.
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.
Note: Usage of IPv6 Unnumbered has the same issue as [RFC8029],
described in Section 3.4.2 of [RFC7439]. A solution should be
considered an applied to both [RFC8029] and this document.
10.1. Sub-TLVs
This section defines the sub-TLVs that MAY be included as part of the
Detailed Interface and Label Stack TLV. Two sub-TLVs are defined:
Sub-Type Sub-TLV Name
--------- ------------
1 Incoming Label stack
2 Incoming Interface Index
10.1.1. Incoming Label Stack Sub-TLV
The Incoming Label Stack sub-TLV contains the label stack as received
by an LSR. If any TTL values have been changed by this LSR, they
SHOULD be restored.
Incoming Label Stack Sub-TLV Type is 1. Length is variable, and its
format is as below:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Incoming Label Stack Sub-TLV
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10.1.2. Incoming Interface Index Sub-TLV
The Incoming Interface Index object is a Sub-TLV that MAY be included
in a Detailed Interface and Label Stack TLV. The Incoming Interface
Index Sub-TLV describes the index assigned by a local LSR to the
interface which received the MPLS echo request message.
Incoming Interface Index Sub-TLV Type is 2. Length is 8, and its
format is as below:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index Flags | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Incoming Interface Index Sub-TLV
Interface Index Flags
Interface Index Flags field is a bit vector with following format.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero (Reserved) |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
One flag is defined: M. The remaining flags MUST be set to zero
when sending and ignored on receipt.
Flag Name and Meaning
---- ----------------
M LAG Member Link Indicator
When this flag is set, interface index described in
this sub-TLV is a member of a LAG.
Incoming Interface Index
An Index assigned by the LSR to this interface.
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11. Security Considerations
This document extends LSP Traceroute mechanism to discover and
exercise L2 ECMP paths. As a result of supporting the code points
and procedures described in this document, additional processing are
required by initiator LSRs and responder LSRs, especially to compute
and handle the additional multipath information. Due to additional
processing, it is critical that proper security measures described in
[RFC8029] are followed.
The LSP Traceroute allows an initiator LSR to discover the paths of
tested LSPs, providing detailed knowledge of the MPLS network.
Exposing such information to a malicious user is considered
dangerous. To prevent leakage of vital information to untrusted
users, a responder LSR MUST only accept MPLS echo request messages
from trusted sources via filtering source IP address field of
received MPLS echo request messages.[RFC8029] provides additional
recommendations to avoid attacks and recommendations to follow if an
operator desires to prevent tracing.
12. IANA Considerations
12.1. LSR Capability TLV
The IANA is requested to assign new value TBD1 for LSR Capability TLV
from the "Multiprotocol Label Switching Architecture (MPLS) Label
Switched Paths (LSPs) Ping Parameters - TLVs" registry.
Value Meaning Reference
----- ------- ---------
TBD1 LSR Capability TLV this document
12.1.1. LSR Capability Flags
The IANA is requested to create and maintain a registry entitled "LSR
Capability Flags" with following registration procedures:
Registry Name: LAG Interface Info Flags
Bit number Name Reference
---------- ---------------------------------------- ---------
31 D: Downstream LAG Info Accommodation this document
30 U: Upstream LAG Info Accommodation this document
0-29 Unassigned
Assignments of LSR Capability Flags are via Standards Action
[RFC8126].
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12.2. Local Interface Index Sub-TLV
The IANA is requested to assign new value TBD2 (from the range
4-31743) for the Local Interface Index Sub-TLV from the
"Multiprotocol Label Switching Architecture (MPLS) Label Switched
Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV
Types 20" sub-registry.
Value Meaning Reference
----- ------- ---------
TBD2 Local Interface Index Sub-TLV this document
12.2.1. Interface Index Flags
The IANA is requested to create and maintain a registry entitled
"Interface Index Flags" with following registration procedures:
Registry Name: Interface Index Flags
Bit number Name Reference
---------- ---------------------------------------- ---------
15 M: LAG Member Link Indicator this document
0-14 Unassigned
Assignments of Interface Index Flags are via Standards Action
[RFC8126].
Note that this registry is used by the Interface Index Flags field of
following Sub-TLVs:
o The Local Interface Index Sub-TLV which may be present in the
"Downstream Detailed Mapping" TLV.
o The Remote Interface Index Sub-TLV which may be present in the
"Downstream Detailed Mapping" TLV.
o The Incoming Interface Index Sub-TLV which may be present in the
"Detailed Interface and Label Stack" TLV.
12.3. Remote Interface Index Sub-TLV
The IANA is requested to assign new value TBD3 (from the range
32768-49161) for the Remote Interface Index Sub-TLV from the
"Multiprotocol Label Switching Architecture (MPLS) Label Switched
Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV
Types 20" sub-registry.
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Value Meaning Reference
----- ------- ---------
TBD3 Remote Interface Index Sub-TLV this document
12.4. Detailed Interface and Label Stack TLV
The IANA is requested to assign new value TBD4 for Detailed Interface
and Label Stack TLV from the "Multiprotocol Label Switching
Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters -
TLVs" registry ([IANA-MPLS-LSP-PING]).
Value Meaning Reference
----- ------- ---------
TBD4 Detailed Interface and Label Stack TLV this document
12.4.1. Sub-TLVs for TLV Type TBD4
The IANA is requested to create and maintain a sub-registry entitled
"Sub-TLVs for TLV Type TBD4" under "Multiprotocol Label Switching
Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters -
TLVs" registry.
Initial values for this sub-registry, "Sub-TLVs for TLV Types TBD4",
are described below.
Sub-Type Name Reference
----------- -------------------------------------- ---------
1 Incoming Label Stack this document
2 Incoming Interface Index this document
3-16383 Unassigned (mandatory TLVs)
16384-31743 Experimental
32768-49161 Unassigned (optional TLVs)
49162-64511 Experimental
Assignments of Sub-Types in the mandatory and optional spaces are via
Standards Action [RFC8126]. Assignments of Sub-Types in the
experimental space is via Specification Required [RFC8126].
12.5. DS Flags
The IANA is requested to assign a new bit number from the "DS flags"
sub-registry from the "Multi-Protocol Label Switching (MPLS) Label
Switched Paths (LSPs) Ping Parameters - TLVs" registry
([IANA-MPLS-LSP-PING]).
Note: the "DS flags" sub-registry is created by [RFC8029].
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Bit number Name Reference
---------- ---------------------------------------- ---------
TBD5 G: LAG Description Indicator this document
13. Acknowledgements
The authors would like to thank Nagendra Kumar, Sam Aldrin, for
providing useful comments and suggestions. The authors would like to
thank Loa Andersson for performing a detailed review and providing
number of comments.
The authors also would like to extend sincere thanks to the MPLS RT
review members who took time to review and provide comments. The
members are Eric Osborne, Mach Chen and Yimin Shen. The suggestion
by Mach Chen to generalize and create the LSR Capability TLV was
tremendously helpful for this document and likely for future
documents extending the MPLS LSP Ping and Traceroute mechanism. The
suggestion by Yimin Shen to create two separate validation procedures
had a big impact to the contents of this document.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
14.2. Informative References
[IANA-MPLS-LSP-PING]
IANA, "Multi-Protocol Label Switching (MPLS) Label
Switched Paths (LSPs) Ping Parameters",
<http://www.iana.org/assignments/mpls-lsp-ping-parameters/
mpls-lsp-ping-parameters.xhtml>.
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[IEEE802.1AX]
IEEE Std. 802.1AX, "IEEE Standard for Local and
metropolitan area networks - Link Aggregation", November
2008.
[RFC7439] George, W., Ed. and C. Pignataro, Ed., "Gap Analysis for
Operating IPv6-Only MPLS Networks", RFC 7439,
DOI 10.17487/RFC7439, January 2015,
<https://www.rfc-editor.org/info/rfc7439>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Appendix A. LAG with intermediate L2 Switch Issues
Several flavors of "LAG with L2 switch" provisioning models and the
corresponding MPLS data plane ECMP traversal validation issues are
described in this section .
A.1. Equal Numbers of LAG Members
R1 ==== S1 ==== R2
The issue with this LAG provisioning model is that packets traversing
a LAG member from Router 1 (R1) to intermediate L2 switch (S1) can
get load balanced by S1 towards Router 2 (R2). Therefore, MPLS echo
request messages traversing a specific LAG member from R1 to S1 can
actually reach R2 via any of the LAG members, and the sender of MPLS
echo request messages has no knowledge of this nor no way to control
this traversal. In the worst case, MPLS echo request messages with
specific entropies to exercise every LAG members from R1 to S1 can
all reach R2 via same LAG member. Thus it is impossible for MPLS
echo request sender to verify that packets intended to traverse
specific LAG member from R1 to S1 did actually traverse that LAG
member, and to deterministically exercise "receive" processing of
every LAG member on R2.
A.2. Deviating Numbers of LAG Members
____
R1 ==== S1 ==== R2
There are deviating number of LAG members on the two sides of the L2
switch. The issue with this LAG provisioning model is the same as
previous model, sender of MPLS echo request messages have no
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knowledge of L2 load balance algorithm nor entropy values to control
the traversal.
A.3. LAG Only on Right
R1 ---- S1 ==== R2
The issue with this LAG provisioning model is that there is no way
for MPLS echo request sender to deterministically exercise both LAG
members from S1 to R2. And without such, "receive" processing of R2
on each LAG member cannot be verified.
A.4. LAG Only on Left
R1 ==== S1 ---- R2
MPLS echo request sender has knowledge of how to traverse both LAG
members from R1 to S1. However, both types of packets will terminate
on the non-LAG interface at R2. It becomes impossible for MPLS echo
request sender to know that MPLS echo request messages intended to
traverse a specific LAG member from R1 to S1 did indeed traverse that
LAG member.
Authors' Addresses
Nobo Akiya
Big Switch Networks
Email: nobo.akiya.dev@gmail.com
George Swallow
Cisco Systems
Email: swallow@cisco.com
Stephane Litkowski
Orange
Email: stephane.litkowski@orange.com
Bruno Decraene
Orange
Email: bruno.decraene@orange.com
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John E. Drake
Juniper Networks
Email: jdrake@juniper.net
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
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