Network Working Group Sami Boutros
INTERNET-DRAFT Siva Sivabalan
Intended Status: Standards Track George Swallow
Shaleen Saxena
Cisco Systems
Vishwas Manral
Hewlett Packard Co.
Sam Aldrin
Huawei Technologies, Inc.
Expires: September 25, 2014 March 24, 2014
Definition of Time-to-Live TLV for LSP-Ping Mechanisms
draft-ietf-mpls-lsp-ping-ttl-tlv-07.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.
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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Boutros Expires September 25, 2014 [Page 1]
INTERNET DRAFT Lsp-ping-ttl-tlv March 24, 2014
Copyright and License Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Time To Live TLV . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. TTL TLV Format . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Traceroute mode . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Error scenario . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1 Normative References . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
Boutros Expires September 25, 2014 [Page 2]
INTERNET DRAFT Lsp-ping-ttl-tlv March 24, 2014
1. Introduction
A MS-PW may 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 reply
back to the sender without knowing the hop-count distance of the
originator. 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, 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 defined 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.
This mechanism only works if the echo reply is sent down the co-
routed LSP, hence the scope of this TTL TLV is currently limited to
MS-PW or Bidirectional co-routed MPLS LSPs. The presence of the TLV
implies the use of the return path of the co-routed LSP, if the
return path is any other mechanism then the TLV in the echo request
MUST be ignored.
2. Terminology
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].
LSR: Label Switching Router
MPLS-TP: MPLS Transport Profile
MS-PW: Multi-Segment Pseudowire
PW: Pseudowire
Boutros Expires September 25, 2014 [Page 3]
INTERNET DRAFT Lsp-ping-ttl-tlv March 24, 2014
TLV: Type Length Value
TTL: Time To Live
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 flag; the rest of the
flags are currently undefined and must be zero (MBZ) 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
understand the TTL TLV, it will simply ignore the TLV (Type value of
Boutros Expires September 25, 2014 [Page 4]
INTERNET DRAFT Lsp-ping-ttl-tlv March 24, 2014
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
choice of the value 2 will be based on the operator input requesting
the echo request or from the optional LDP switching point TLV. 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.
Boutros Expires September 25, 2014 [Page 5]
INTERNET DRAFT Lsp-ping-ttl-tlv March 24, 2014
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 intercepted before
the intended destination for reason other than label TTL expiry. 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, the label TTL value used in the Echo Reply packet
must be modified by deducting the incoming label TTL on the received
packet from TTL TLV value. If the echo request packet is punted to
the CPU before the incoming label TTL is deducted, then another 1
must be deducted. In other words:
Return TTL Value on the Echo Reply packet = (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.
The recommendation in [RFC4379] security section applies, to check
the source address of the MPLS echo request, however the source
address can now be any node along the LSP path.
A faulty transit node changing the TTL TLV value could make the wrong
node reply to the MPLS echo request, and/or the wrong node to receive
the MPLS echo reply. An LSP trace may help identify the faulty
transit node.
6. IANA Considerations
Boutros Expires September 25, 2014 [Page 6]
INTERNET DRAFT Lsp-ping-ttl-tlv March 24, 2014
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). The value must be assigned from the
range (32768-49161) of optional TLVs.
7. Acknowledgements
The authors would like to thank Greg Mirsky for his 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.
Authors' 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
Boutros Expires September 25, 2014 [Page 7]
INTERNET DRAFT Lsp-ping-ttl-tlv March 24, 2014
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
Hewlett Packard Co.
19111 Pruneridge Ave,
Cupertino, CA 95014 USA
United States
EMail: vishwas.manral@hp.com
Michael Wildt
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough , MASSACHUSETTS 01719
United States
Email: mwildt@cisco.com
Sam Aldrin
Huawei Technologies, Inc.
1188 Central Express Way,
Santa Clara, CA 95051
United States
Email: aldrin.ietf@gmail.com
Boutros Expires September 25, 2014 [Page 8]