| Internet Engineering Task Force | N. Akiya |
| Internet-Draft | G. Swallow |
| Updates: 4379,6790 (if approved) | C. Pignataro |
| Intended status: Standards Track | Cisco Systems |
| Expires: June 19, 2014 | December 16, 2013 |
Label Switched Path (LSP) Ping/Trace over MPLS Network using Entropy Labels (EL)
draft-akiya-mpls-entropy-lsp-ping-01
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.
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 and RFC6790.
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/.
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This Internet-Draft will expire on June 19, 2014.
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Section 3.3.1 of [RFC4379] specifies multipath information encoding 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.
With introduction of [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: [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.
These scenarios will be quite common because every deployment of
As pointed out in [RFC6790] the procedures of [RFC4379] with respect to multipath information type {9} are incomplete. However [RFC6790] does not actually update [RFC4379]. Further the specific EL location is not clearly defined, particularly in the case of Flow-Aware Transport Pseudowires [RFC6391]. This document defines a new FEC Stack sub-TLV for the Entropy Label. Section 3 of this document updates the procedures for multipath information type {9} described in [RFC4379] Rest of this document describes extensions required to restore ECMP discovery and tracing capabilities for scenarios described.
[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.
LSP Ping initiating LSR sends MPLS echo request with multipath information. This multipath information is described in DSMAP/DDMAP TLV of echo request, and can contain set of IP addresses or set of labels today. 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) is to determine 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.
Current behavior is problematic in following scenarios: [RFC6790]. Therefore, this document defines a multipath information type to be used in the DSMAP/DDMAP of MPLS echo request/reply packets in Section 8.
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
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.
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 Section 7.
[RFC4379] defined multipath type {9} for tracing of LSPs where label based load-balancing is used. However, as pointed out in [RFC6790], the procedures for using this type are incomplete. First, the specific location of the label was not defined. What was assumed, but not spelled out, was that the presence of multipath type {9} meant the responder should act as if the payload of the received packet were non-IP and that the bottom-of-stack label should be replaced by the values indicated by multipath type {9} to determine their respective out-going interfaces.
Further, with the introduction of [RFC6790], entropy labels may now appear anywhere in a label stack.
This section defines to which labels multipath type {9} can apply. Additionally it defines procedures for tracing pseudowires and flow-aware pseudowires. These procedures pertain to the use of multipath information type {9} as well as type {10}.
Section 6 defines a new FEC-Stack sub-TLV to indicate and entropy label. Multipath type {9} applies exclusively to this sub-TLV. Any LSP Ping message containing a DD-MAP or DS-MAP with multipath type {9} MUST include an EL_FEC at the bottom of the FEC-Stack.
When an MPLS echo request message is received containing a FEC-Stack with an EL-FEC at the bottom of the FEC stack and is not preceded by an entropy label, the responder must behave (for load balancing purposes) as if the first word of the message were a Pseudowire Control Word.
In order to trace a non-FAT pseudowire, instead of including the appropriate PW-FEC in the FEC-Stack, an EL-FEC is included. 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 at transport layer (e.g. LDP and/or RSVP). 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.
In order to trace a Flow-Aware Transport Pseudowire, the initiator includes an EL-FEC at the bottom of the FEC-Stack and pushes the appropriate PW-FEC onto the FEC-Stack.
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.
In addition to procedures described in [RFC4379] as updated by Section 3 and [RFC6424], initiating LSR MUST operate with following procedures.
In following conditions, initiating LSR may have lost the ability to exercise specific ECMP paths. Initiating LSR MAY continue with "best effort".
Common Procedures: Responder LSR receiving MPLS echo request packet with multipath information type {10} MUST validate following contents. Any deviation MUST result in responder LSR to consider the packet as malformed and return code 1 (Malformed echo request received) in MPLS echo reply packet.
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 responder LSR performs deviating load balance techniques per downstream basis, appropriate procedures matching to each downstream load balance technique MUST be operated.
Stitching LSR that xconnects Flow-Aware Transport Pseudowires behave in one of two ways:
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.
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: FAT-PW [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.
The Length is 4. Labels are 20-bit values treated as numbers.
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
DS Flags
--------
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |L|E|I|N|
+-+-+-+-+-+-+-+-+
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.
One new multipath information type is added to be used in DSMAP/DDMAP TLVs. New multipath type has value of 10.
Key Type Multipath Information --- ---------------- --------------------- 10 IP and label set IP addresses and label prefixes
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.
Multipath information type 10 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |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) | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
There are couple of scenarios where LSP path tracing mechanics are not supported in this draft revision.
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 [RFC4379] and [RFC6424] are followed.
[RFC4379] defines the Downstream Mapping TLV, which has the Type 2 assigned from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry. [RFC6424] defines the Downstream Detailed Mapping TLV, which has the Type 20 assigned from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry. Both TLVs shares two fields: "DS Flags" and "Multipath Type". This document requires allocation of new values in both the "DS Flags" and "Multipath Type" fields, which are not maintained by IANA today. Therefore, this document requests IANA to create new registries within [IANA-MPLS-LSP-PING] protocol to maintain "DS Flags" and "Multipath Type" fields. Name of registries and initial values are described in immediate sub-sections to follow.
Bit number Name Reference
---------- ---------------------------------------- ---------
7 N: Treat as a Non-IP Packet RFC4379
6 I: Interface and Label Stack Object Request RFC4379
5 E: ELI/EL push indicator this document
4 L: Label based load balance indicator this document
3-0 Unassigned
Note that "DS Flags" is a field included in two TLVs defined in "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry: Downstream Mapping TLV (value 2) and Downstream Detailed Mapping TLV (value 20). Modification to "DS Flags" registry will affect both TLVs.
Value Meaning Reference
---------- ---------------------------------------- ---------
0 no multipath RFC4379
1 Unassigned
2 IP address RFC4379
3 Unassigned
4 IP address range RFC4379
5-7 Unassigned
8 Bit-masked IP address set RFC4379
9 Bit-masked label set RFC4379
10 IP and label set this document
11-255 Unassigned
Note that "Multipath Type" is a field included in two TLVs defined in "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry: Downstream Mapping TLV (value 2) and Downstream Detailed Mapping TLV (value 20). Modification to "Multipath Type" registry will affect both TLVs.
IANA is requested to assign a new sub-TLV from the "Sub-TLVs for TLV Types 1 and 16" section from "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry.
Sub-Type Sub-TLV Name Reference
-------- ------------ ---------
TBD1 Entropy Label FEC this document
Authors would like to thank Loa Andersson for performing thorough review and providing valuable comments.
Nagendra Kumar
Cisco Systems
Email: naikumar@cisco.com
| [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. |
| [RFC6790] | Kompella, K., Drake, J., Amante, S., Henderickx, W. and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, November 2012. |
| [RFC6424] | Bahadur, N., Kompella, K. and G. Swallow, "Mechanism for Performing Label Switched Path Ping (LSP Ping) over MPLS Tunnels", RFC 6424, November 2011. |
| [RFC6391] | Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan, J. and S. Amante, "Flow-Aware Transport of Pseudowires over an MPLS Packet Switched Network", RFC 6391, November 2011. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. |
| [I-D.ravisingh-mpls-el-for-seamless-mpls] | Singh, R., Shen, Y. and J. Drake, "Entropy label for seamless MPLS", Internet-Draft draft-ravisingh-mpls-el-for-seamless-mpls-01, October 2013. |
| [IANA-MPLS-LSP-PING] | IANA, "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters", . |