Network Working Group S. Boutros, Ed.
Internet-Draft S. Sivabalan, Ed.
Intended status: Standards Track S. Saxena, Ed.
Expires: August 27, 2011 Cisco Systems
V. Manral, Ed.
IPInfusion Inc.
G. Swallow
Cisco Systems
February 27, 2011
Definition of Time-to-Live TLV for LSP-Ping Mechanisms
draft-boutros-mpls-lsp-ping-ttl-tlv-03.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. Similar shortcoming is seen on a bidirectional co-
routed MPLS TP LSPs. This document defines a TLV to address these
shortcomings.
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.
Internet-Drafts are working documents of the Internet Engineering
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other groups may also distribute working documents as Internet-
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Time To Live TLV...............................................4
4. Operation......................................................5
5. Security Considerations........................................6
6. IANA Considerations............................................7
7. Acknowledgements...............................................7
8. References.....................................................7
8.1. Normative References......................................7
8.2. Informative References....................................7
Author's Addresses................................................8
1. Introduction
An 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 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
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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.
In MPLS networks (also applicable to MPLS-TP) for bidirectional co-
routed LSP's, 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.
The scope of this TTL TLV is currently limited to MS-PW or
Bidirectional co-routed MPLS TP LSPs.
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 Error!
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
3.1. TTL TLV 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 = TBD | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value | Reserved | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Time To Live TLV format
The TTL TLV has the format shown in Figure 1.
Value
The value of the TTL as specified by this TLV
Flags
The Flags field is a bit vector with the following format:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ |R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
One flag is defined for now, the R bit; the rest MUST be set to
zero when sending and ignored on receipt.
The R flag (Reply TTL) is set signify that the value is meant
to be used as the TTL for the reply packet. Other bits may be
defined later to enhance the scope of this TLV.
3.2. Usage
This TLV shall be included in the echo request by the originator of
request. The use of this TLV is optional. If a receiver does not
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understand the TTL TLV, it will simply ignore the TLV (Type value of
TLV is assumed to be in the range of optional TLV's 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, and if the value field is zero, the LSP Ping Echo
request packet SHOULD be dropped.
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 other words, if the
value of the TTL provided by this TLV does not match the TTL
determined by other means, such as Switching Point TLV in MS-PW, then
TTL TLV must be used. This will aid the originator of the echo
request in analyzing the return path.
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
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.
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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.
4.1. Traceroute mode
In the traceroute mode TTL value in the TLV is successively set to 1,
2, and so on. This is similar to the TTL values used for the label
set on the packet.
4.2. Error scenario
It is possible that the echo request packet was punted before the
intended destination. This could be due network faults,
misconfiguration or other reasons. In such cases, if the return TTL
is set to the value specified in the TTL TLV then the echo response
packet will continue beyond the originating node. This becomes a
security issue.
To prevent this issue, the TTL value used must be modified by
deducting the incoming label TTL. If the echo request packet is
punted before the incoming TTL is deducted, then another 1 must be
deducted. In other words:
Return TTL Value = (TTL TLV Value)-(Incoming Label TTL)-1
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.
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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.
Optional Time To Live TLV (See Section 3). The Suggested value is
32769 as suggested by RFC 4379 Section 3.
7. Acknowledgements
The authors would like to thank Greg Mirsky, Laxmi Narasimaha Reddy
Devireddy and Mahesh Akula for their comments.
8. References
8.1. Normative References
[1] K. Kompella, G. Swallow, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February
2006.
[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.
8.2. Informative References
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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
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
George Swallow
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MASSACHUSETTS 01719
United States
Email: swallow@cisco.com
Michael Wildt
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough , MASSACHUSETTS 01719
United States
Email: mwildt@cisco.com
Sam Aldrin
Huawei Technologies, co.
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2330 Central Express Way,
Santa Clara, CA 95051, USA
Email: aldrin.ietf@gmail.com
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