Network Working Group Siva Sivabalan (Ed.)
Internet Draft Sami Boutros (Ed.)
Intended status: Standards Track George Swallow
Expires: September 2012 Shaleen Saxena
Cisco Systems, Inc.
Vishwas Manral
IPInfusion, Inc.
Sam Aldrin
Huawei Technologies, Inc.
March 7, 2012
Definition of Time-to-Live TLV for LSP-Ping Mechanisms
draft-ietf-mpls-lsp-ping-ttl-tlv-02.txt
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
shortcoming.
Requirements Language
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 [3].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Time To Live TLV...............................................4
4. Operation......................................................4
5. Security Considerations........................................5
6. IANA Considerations............................................5
7. References.....................................................5
7.1. Normative References......................................5
7.2. Informative References.........Error! Bookmark not defined.
Author's Addresses................................................7
1. Introduction
A MS-PW 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 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
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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.
In MPLS networks (also applicable to MPLS-TP), for bidirectional co-
routed LSPs, if it is desired to verify connectivity from any
intermediate node (LSR) on the LSP to the any other LSR on the LSP
the receiver may need to know the TTL to send the Echo reply with, so
as the packet is intercepted by 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 or Bidirectional LSP.
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-2119Error!
Reference source not found.
2. Terminology
LSR: Label Switching Router
MPLS-OAM: MPLS Operations, Administration and Maintenance
MPLS-TP: MPLS Transport Profile
MS-PW: Multi-Segment PseudoWire
PW: PseudoWire
TLV: Type Length Value
TTL: Time To Live
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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. 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 will simply ignore
the TLV (Type value of TLV is assumed to be in the range of optional
TLVs which SHOULD be ignored if an implementation does not support or
understand them). 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.
If a receiver understands the TTL TLV, and the TTL TLV is present in
the echo request, the receiver MUST use the TTL value specified in
TLV in the MPLS header of the echo reply.
In the traceroute mode TTL value in the TLV is successively set to 1,
2, and so on.
4. Operation
In this section, we explain a use case for the TTL TLV with an MPLS
MS-PW.
<------------------MS-PW --------------------->
A B C D E
o -------- o -------- o --------- o --------- o
------Echo Request----->
<-----Echo Reply--------
Figure 2: Use-case with MS-PWs
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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.
The same operation will apply in the case a co-routed bidirectional
LSP and we want to check connectivity from an intermediate LSR B to
another LSR D, from B.
5. Security Considerations
This draft allows the setting of the TTL value in the MPLS Label of
an echo reply, so that it can be intercepted by an intermediate
device. This can cause a device to get a lot of LSP Ping packets
which get redirected to the CPU.
However the same is possible even without the changes mentioned in
this document. A device should rate limit the LSP ping packets
redirected to the CPU so that the CPU is not overwhelmed.
6. IANA Considerations
IANA is requested to assign TLV type value to the following TLV from
the "Multiprotocol Label Switching Architecture (MPLS) Label Switched
Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub-
registry.
Time To Live TLV (See Section 3).
7. References
7.1. Normative References
[1] K. Kompella, G. Swallow, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February
2006.
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[2] T. Nadeau, et. al, "Pseudowire Virtual Circuit Connectivity
Verification (VCCV): A Control Channel for Pseudowires ", RFC
5085, December 2007.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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Author's Addresses
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario, K2K 3E8
Canada
Email: msiva@cisco.com
Sami Boutros
Cisco Systems, Inc.
3750 Cisco Way
San Jose, California 95134
USA
Email: sboutros@cisco.com
George Swallow
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MASSACHUSETTS 01719
United States
Email: swallow@cisco.com
Shaleen Saxena
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough , MASSACHUSETTS 01719
United States
Email: ssaxena@cisco.com
Vishwas Manral
IPInfusion, Inc.
1188 E. Arques Ave.,
Sunnyvale, CA 94085
United States
Email: vishwas@ipinfusion.com
Sam Aldrin
Huawei Technologies, Inc.
1188 Central Express Way,
Santa Clara, CA 95051
United States
Email: aldrin.ietf@gmail.com
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