Network Working Group Sami Boutros (Ed.)
Internet Draft Siva Sivabalan (Ed.)
Intended status: Standards Track George Swallow
Expires: September 2010
Cisco Systems, Inc.
March 1, 2010
Definition of Time-to-Live TLV for LSP-Ping Mechanisms
draft-boutros-mpls-lsp-ping-ttl-tlv-00.txt
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Abstract
LSP-Ping is a widely deployed Operation, Administration, and
Maintenance (OAM) mechanism in MPLS networks. However, in the present
form, this mechanism is inadequate to verify connectivity of a
segment of a Multi-Segment PseudoWire (MS-PW) from any node on the
path of the MS-PW. This document defines a TLV to address this
shortcomming.
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Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Time To Live TLV...............................................3
4. Operation......................................................3
5. Security Considerations........................................4
6. IANA Considerations............................................4
7. References.....................................................4
7.1. Normative References......................................4
7.2. Informative References....................................5
Author's Addresses................................................5
Full Copyright Statement..........................................5
Intellectual Property Statement...................................6
1. Introduction
A MS-PW [4] can span across multiple service provider networks. In
order to allow Service Providers (SP) to verify segments of such MS-
PW from any node on the path of the MS-PW, any node along the path of
the MS-PW, should be able to originate an LSP-Ping [2][3] echo
request packet to any another node along the path of the MS-PW and
receive the corresponding echo reply. If the originator of the echo
request is at the end of a MS-PW, the receiver of the request can
send the reply back to the sender without knowing the hop-count
distance of the originator. For example, the reply will be
intercepted by the originator regardless of the TTL value on the
reply packet. But, if the originator is not at the end of the MS-PW,
the receiver of the echo request MAY need to know how many hops away
the originator of the echo request is so that it can set the TTL
value on the MPLS header for the echo reply to be intercepted at the
originator node.
A new optional TTL TLV is being proposed in this document this TLV
will be added by the originator of the echo request to inform the
receiver how many hops away the originator is on the path of the MS-
PW.
Conventions used in this document
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 [1].
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2. Terminology
LSR: Label Switching Router
MPLS-OAM: MPLS Operations, Administration and Maintenance
MS-PW: Multi-Segment PseudoWire
PW: PseudoWire
TLV: Type Length Value
TTL: Time To Live
3. Time To Live TLV
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 = TBD | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| value |
+-+-+-+-+-+-+-+-+
Figure 1: Time To Live TLV format
The TTL TLV has the format shown in Figure 1. This TLV shall be
included in the echo request by the originator of request. If a TTL
TLV is present in the echo request, the LSR processing the echo
request MUST use the TTL value specified in TLV in the MPLS header of
the echo reply.
The use of this TLV is optional. If the value field is zero, the LSP
Ping Echo request packet will be dropped.
If a receiver does not understand the TTL TLV, it can simply ignore
the TLV. In the absence of TTL TLV or if TTL TLV is ignored by a
receiver, the determination of the TTL value used in the MPLS label
on the echo reply is beyond the scope of this document.
4. Operation
In this section, we explain a use case for the TTL TLV with an MPLS
MS-PW.
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<------------------MS-PW --------------------->
A B C D E
o -------- o -------- o --------- o --------- o
------Echo Request----->
<-----Echo Reply--------
Figure 2: Use-case with MS-PWs
Let us assume a MS-PW going through LSRs A, B, C, D, and E.
Furthermore, assume that an operator wants to perform a connectivity
check between B and D from B. Thus, an LSP-Ping request with the TTL
TLV is originated from B and sent towards D. The echo request packet
contains the FEC of the PW Segment between C and D. The value field
of the TTL TLV and the TTL field of the MPLS label are set to 2. The
echo request is intercepted at D because of TTL expiry. D detects the
TTL TLV in the request, and use the TTL value (i.e., 2) specified in
the TLV on the MPLS label of the echo reply. The echo reply will be
intercepted by B because of TTL expiry.
5. Security Considerations
TBD
6. IANA Considerations
IANA maintains the registry for the Type field of top-level TLVs as
well as any associated sub-TLVs. IANA is requested to assign a new
Type value for the TTL TLV defined in this document. The suggested
value is 11.
7. References
7.1. Normative References
[1] Bradner. S, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March, 1997.
[2] K. Kompella, G. Swallow, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.
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[3] T. Nadeau, et. al, "Pseudowire Virtual Circuit Connectivity
Verification (VCCV): A Control Channel for Pseudowires ", RFC
5085, December 2007.
7.2. Informative References
[4] Nabil Bitar, et. al, "Requirements for Multi-Segment Pseudowire
Emulation Edge-to-Edge (PWE3)", RFC5254, October 2008.
Author's Addresses
Sami Boutros
Cisco Systems, Inc.
3750 Cisco Way
San Jose, California 95134
USA
Email: sboutros@cisco.com
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario, K2K 3E8
Canada
Email: msiva@cisco.com
George Swallow
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MASSACHUSETTS 01719
United States
Email: swallow@cisco.com
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