| Internet Engineering Task Force | N. Akiya |
| Internet-Draft | G. Swallow |
| Updates: 4379,6424 (if approved) | Cisco Systems |
| Intended status: Standards Track | S. Litkowski |
| Expires: April 25, 2015 | B. Decraene |
| Orange | |
| J. Drake | |
| Juniper Networks | |
| October 22, 2014 |
Label Switched Path (LSP) Ping/Trace Multipath Support for Link Aggregation Group (LAG) Interfaces
draft-akiya-mpls-lsp-ping-lag-multipath-02
This document defines an extension to the Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Ping and Traceroute to describe Multipath Information for Link Aggregation (LAG) member links separately, thus allowing MPLS LSP Ping and Traceroute to discover and exercise specific paths of layer 2 (L2) Equal-Cost Multipath (ECMP) over LAG interfaces.
This document updates RFC4379 and RFC6424.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
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 http://datatracker.ietf.org/drafts/current/.
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 25, 2015.
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.
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The following acronyms/terminologies are used in this document:
The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Ping and Traceroute [RFC4379] are powerful tools designed to diagnose all available layer 3 (L3) paths of LSPs, i.e. provides diagnostic coverage of L3 Equal-Cost Multipath (ECMP). In many MPLS networks, Link Aggregation (LAG) as defined in [IEEE802.1AX], which provide layer 2 (L2) ECMP, are often used for various reasons. MPLS LSP Ping and Traceroute tools were not designed to discover and exercise specific paths of L2 ECMP. Result raises a limitation for following scenario when LSP X traverses over LAG Y:
With above scenario, MPLS LSP Ping and Traceroute will not be able to detect the MPLS switching failure of problematic member link(s) of the LAG. In other words, lack of L2 ECMP discovery and exercise capability can produce an outcome where MPLS LSP Ping and Traceroute can be blind to MPLS switching failures over LAG interface that are impacting MPLS traffic. It is, thus, desirable to extend the MPLS LSP Ping and Traceroute to have deterministic diagnostic coverage of LAG interfaces.
This document defines an extension to the MPLS LSP Ping and Traceroute to describe Multipath Information for LAG member links separately, thus allowing MPLS LSP Ping and Traceroute to discover and exercise specific paths of L2 ECMP over LAG interfaces. Reader is expected to be familiar with mechanics of the MPLS LSP Ping and Traceroute described in Section 3.3 of [RFC4379] and Downstream Detailed Mapping TLV (DDMAP) described in Section 3.3 of [RFC6424].
MPLS echo request carries a DDMAP and an optional TLV to indicate that separate load balancing information for each L2 nexthop over LAG is desired in MPLS echo reply. Responder LSR places the same optional TLV in the MPLS echo reply to provide acknowledgement back to the initiator. It also adds, for each downstream LAG member, a load balance information (i.e. multipath information and interface index). For example:
<----- LDP Network ----->
+-------+
| |
A-------B=======C-------E
| |
+-------D-------+
---- Non-LAG
==== LAG comprising of two member links
Figure 1: Example LDP Network
This document defines:
Note that the mechanism described in this document does 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 MPLS echo request carries a DDMAP and the LAG Interface Info TLV (described in Section 5) to indicate that separate load balancing information for each L2 nexthop over LAG is desired in MPLS echo reply. Responder LSRs that understand the LAG Interface Info TLV but unable to describe outgoing LAG member links separately MUST add the LAG Interface Info TLV in the MPLS echo reply to provide acknowledgement back to the initiating LSR. The Downstream LAG Info Accommodation flag MUST NOT be set in LAG Interface Info Flags. The responder LSRs that understands the LAG Interface Info TLV and able to describe outgoing LAG member links separately MUST use the follow procedures, regardless of whether or not outgoing interfaces include LAG interfaces:
When both the Interface Index Sub-TLV and the Multipath Data Sub-TLV is placed in the DDMAP to describe a LAG member link, Interface Index Sub-TLV MUST be added first with Multipath Data Sub-TLV immediately following.
For example, 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index Sub-TLV of LAG member link #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multipath Data Sub-TLV LAG member link #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index Sub-TLV of LAG member link #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multipath Data Sub-TLV LAG member link #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Stack Sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Example of DDMAP in MPLS Echo Reply
When an initiating LSR receives a DDMAP containing LAG member information from a downstream LSR with TTL=n, then the subsequent DDMAP sent by the initiating LSR to the downstream LSR with TTL=n+1 through a particular LAG member link MUST be updated with following procedures:
Using the DDMAP example described in the Figure 2, the DDMAP being sent by the initiating LSR through LAG member link #1 to the next downstream LSR should be:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multipath Data Sub-TLV LAG member link #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Stack Sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Example of DDMAP in MPLS Echo Request
This document does not update the FEC validation procedures nor the DDMAP validation procedures. Rather this document provides the mechanism for the initiating LSR to obtain additional information from the downstream LSRs when incoming and/or outgoing interfaces are LAGs. With this additional information, it is the responsibility of the initiating LSR to validate the L2 ECMP traversal.
The MPLS echo request is sent with a DDMAP with DS Flags I set and the optional LAG Interface Info TLV 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. Responder LSRs that understands the LAG Interface Info TLV but unable to describe incoming LAG member link MUST add the LAG Interface Info TLV in the MPLS echo reply to provide acknowledgement back to the initiator. The Upstream LAG Info Accommodation flag MUST NOT be set in LAG Interface Info Flags. The responder LSRs that understands the LAG Interface Info TLV and able to describe incoming LAG member link MUST use the following procedures, regardless of whether or not incoming interface was a LAG interface: Section 3, described procedures in this section will allow an initiating LSR to know:
These procedures allow initiating LSR to:
Along with procedures described in
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.
With additional logics added in the initiating LSR, following checks can be performed: Appendix A. LAG provisioning models in operated network should be considered when analyzing the output of LSP Traceroute exercising L2 ECMPs.
Note that defined procedures will provide a deterministic result for LAG interfaces that are back-to-back connected between routers (i.e. no L2 switch in between). If there is a L2 switch between LSR at TTL=n and LSR at TTL=n+1, there is no guarantee that traversal of every LAG member link at TTL=n will result in reaching different interface index at TTL=n+1. Issues resulting from LAG with L2 switch in between are further described in
The LAG Interface Info object is a new TLV that MAY be included in the MPLS echo request message. An MPLS echo request MUST NOT include more than one LAG Interface Info object. Presence of LAG Interface Info object is a request that responder LSR describes upstream and downstream LAG interfaces according to procedures defined in this document. If the responder LSR is able to accommodate this request, then the LAG Interface Info object MUST be included in the MPLS echo reply message.
LAG Interface Info TLV Type is TBD1. Length is 4. The Value field of LAG Interface 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LAG Interface Info Flags | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: LAG Interface Info TLV
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero (Reserved) |U|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flag Name and Meaning
---- ----------------
U Upstream LAG Info Accommodation
When this flag is set, LSR is capable of placing Incoming
Interface Index Sub-TLV, describing LAG member link, in
the Detailed Interface and Label Stack TLV.
D Downstream LAG Info Accommodation
When this flag is set, LSR is capable of placing Interface
Index Sub-TLV and Multipath Data Sub-TLV, describing LAG
member link, in the Downstream Detailed Mapping TLV.
One flag, G, is added in DS Flags field of the DDMAP TLV. In the MPLS echo request message, G flag MUST be cleared when sending, and ignored on receipt. In the MPLS echo reply message, G flag MUST be set if the DDMAP TLV describes a LAG interface. It MUST be cleared otherwise.
DS Flags
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |G|MBZ|I|N|
+-+-+-+-+-+-+-+-+
Flag Name and Meaning
---- ----------------
G LAG Description Indicator
When this flag is set, DDMAP describes a LAG interface.
The Interface Index object is a Sub-TLV that MAY be included in a DDMAP TLV. Zero or more Interface Index object MAY appear in a DDMAP TLV. The Interface Index Sub-TLV describes the index assigned by local LSR to the egress interface.
Interface Index Sub-TLV Type is TBD2. Length is 8, and the Value field 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index Flags | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Interface Index Sub-TLV
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero (Reserved) |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flag Name and Meaning
---- ----------------
M LAG Member Link Indicator
When this flag is set, interface index described in
this sub-TLV is member of a LAG.
Interface Index
The Detailed Interface and Label Stack object is a TLV that MAY be included in a 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. This TLV allows the initiating 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 TBD3. Length is K + Sub-TLV Length, and the Value field 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Sub-TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. List of Sub-TLVs .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Detailed Interface and Label Stack TLV
Type # Address Type K Octets
------ ------------ --------
1 IPv4 Numbered 16
2 IPv4 Unnumbered 16
3 IPv6 Numbered 40
4 IPv6 Unnumbered 28
This section defines the sub-TLVs that MAY be included as part of the Detailed Interface and Label Stack TLV.
Sub-Type Value Field
--------- ------------
1 Incoming Label stack
2 Incoming Interface Index
The Incoming Label Stack sub-TLV contains the label stack as received by the 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 the Value field 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Incoming Label Stack 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 this LSR to the interface which received the MPLS echo request message.
Incoming Interface Index Sub-TLV Type is 2. Length is 8, and the Value field 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index Flags | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Incoming Interface Index Sub-TLV
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero (Reserved) |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flag Name and Meaning
---- ----------------
M LAG Member Link Indicator
When this flag is set, the interface index described in
this sub-TLV is a member of a LAG.
Interface Index
This document extends LSP Traceroute mechanism to discover and exercise L2 ECMP paths. Additional processing are required for initiating LSR and responder LSR, especially to compute and handle increasing number of multipath information. Due to additional processing, it is critical that proper security measures described in [RFC4379] and [RFC6424] are followed.
The IANA is requested to assign new value TBD1 for LAG Interface Info TLV from the "Multiprotocol Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry.
Value Meaning Reference ----- ------- --------- TBD1 LAG Interface Info TLV this document
The IANA is requested to assign new value TBD2 for 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 Interface Index Sub-TLV this document
The IANA is requested to assign new value TBD3 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 ----- ------- --------- TBD3 Detailed Interface and Label Stack TLV this document
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 [I-D.decraene-mpls-lsp-ping-registry].
Bit number Name Reference ---------- ---------------------------------------- --------- TBD4(3) G: LAG Description Indicator this document
The IANA is requested to make a new "Sub-TLVs for TLV Type TBD3" sub-registry 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 TBD3", are described below.
Sub-Type Name Reference --------- ---------------------------------------- --------- 1 Incoming Label Stack this document 2 Incoming Interface Index this document 4-65535 Unassigned
Authors would like to thank Nagendra Kumar and Sam Aldrin for providing useful comments and suggestions.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC4379] | Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006. |
| [RFC6424] | Bahadur, N., Kompella, K. and G. Swallow, "Mechanism for Performing Label Switched Path Ping (LSP Ping) over MPLS Tunnels", RFC 6424, November 2011. |
| [I-D.decraene-mpls-lsp-ping-registry] | Decraene, B., Akiya, N., Pignataro, C., Andersson, L. and S. Aldrin, "IANA registries for LSP ping Code Points", Internet-Draft draft-decraene-mpls-lsp-ping-registry-00, October 2014. |
| [I-D.ietf-mpls-ipv6-only-gap] | George, W. and C. Pignataro, "Gap Analysis for Operating IPv6-only MPLS Networks", Internet-Draft draft-ietf-mpls-ipv6-only-gap-02, August 2014. |
| [IANA-MPLS-LSP-PING] | IANA, "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters", . |
| [IEEE802.1AX] | IEEE Std. 802.1AX, "IEEE Standard for Local and metropolitan area networks - Link Aggregation", November 2008. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. |
Several flavors of "LAG with L2 switch" provisioning models are described in this section, with MPLS data plane ECMP traversal validation issues with each.
R1 ==== S1 ==== R2
____
R1 ==== S1 ==== R2
R1 ---- S1 ==== R2
R1 ==== S1 ---- R2