Network Working Group Neil Hart
Internet Draft Mustapha Aissaoui
Expires: December 2006 Tiberiu Grigoriu
Matthew Bocci
Alcatel
VCCV Extensions for Segmented Pseudo-Wire
draft-hart-pwe3-segmented-pw-vccv-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that
any applicable patent or other IPR claims of which he or she is
aware have been or will be disclosed, and any of which he or she
becomes aware will be disclosed, in accordance with Section 6 of
BCP 79.
This document may only be posted in an Internet-Draft.
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/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on December 19, 2006.
Abstract
This document describes extensions to Single Hop Virtual Circuit
Connectivity Verification (SH-VCCV) procedures for segmented pseudo
Hart et al. Expires December 19, 2006 [Page 1]
Internet-Draft Segmented Pseudo Wire VCCV June 2006
wires to test the end-to-end forwarding datapath and to provide a PW
segment trace capability. This is accomplished by changing the
adaptation function for the Single Hop VCCV parameter at the
switching point between two distinct PW control planes.
Table of Contents
1. Terminology.................................................2
2. Introduction................................................3
2.1. Single Hop VCCV adaptation for end to end verification...4
2.1.1. Inband VCCV using Control Word.....................4
2.2. Single Hop VCCV adaptation for partial tracing from T-PE.5
2.3. VCCV between S-PEs......................................5
3. Security Considerations......................................5
4. IANA Considerations.........................................5
5. Acknowledgments.............................................5
5.1. Normative References....................................6
5.2. Informative References..................................6
Author's Addresses.............................................6
Intellectual Property Statement.................................6
Disclaimer of Validity.........................................7
Copyright Statement............................................7
Acknowledgment.................................................7
1. Terminology
- PW Terminating Provider Edge (T-PE). A PE where the customer-
facing attachment circuits (ACs) are bound to a PW forwarder. A
Terminating PE is present in the first and last segments of a MS-PW.
This incorporates the functionality of a PE as defined in [RFC3985].
- Single-Segment Pseudo Wire (SS-PW). A PW setup directly between two
T-PE devices. Each PW in one direction of a SS-PW traverses one PSN
tunnel that connects the two T-PEs.
- Multi-Segment Pseudo Wire (MS-PW). A static or dynamically
configured set of two or more contiguous PW segments that behave and
function as a single point-to-point PW. Each end of a MS-PW by
definition MUST terminate on a T-PE.
- PW Segment. A part of a single-segment or multi-segment PW, which
is set up between two PE devices, T-PEs and/or S-PEs.
Hart et al. Expires December 19, 2006 [Page 2]
Internet-Draft Segmented Pseudo Wire VCCV June 2006
- PW Switching Provider Edge (S-PE). A PE capable of switching the
control and data planes of the preceding and succeeding PW segments
in a MS-PW. The S-PE terminates the PSN tunnels of the preceding and
succeeding segments of the MS-PW.
- PW switching point for a MS-PW. A PW Switching Point is never the
S-PE and the T-PE for the same MS-PW. A PW switching point runs
necessary protocols to setup and manage PW segments with other PW
switching points and terminating PEs
2. Introduction
Virtual Circuit Connectivity Verification (VCCV) allows network
operators to test the forwarding datapath of pseudo wire (PW)
services. As pseudo wires are extended to cover multiple segments, it
will be important to maintain the facility to verify the forwarding
datapath. Figure 1 illustrates a multi-segment pseudo wire providing
connectivity from T-PE1 to T-PE2 through the switching point S-PE. By
suitable implementation at the S-PEs, VCCV can be simply extended to
provide both end to end and single segment connection verification.
Native |<-----------Pseudo Wire----------->| Native
Layer2 | | Layer2
Service | |<-PSN1-->| |<--PSN2->| | Service
(AC) V V V V V V (AC)
| +----+ +-----+ +----+ |
+----+ | | |=========| |=========| | | +----+
| |----------|........PW1.........|...PW3........|----------| |
| CE1| | | | | | | | | |CE2 |
| |----------|........PW2.........|...PW4........|----------| |
+----+ | |=========| |=========| | +----+
^ +----+ +-----+ +----+ ^
| T-PE1 S-PE T-PE2 |
| |
|<------------------- Emulated Service -------->|
Figure 1 MS-PW Service
In Figure 1 T-PE1 uses the VCCV parameter included in the interface
parameter field of the PW ID FEC TLV or the sub-TLV interface
parameter of the Generalized PW ID FEC TLV to indicate to the far end
T-PE2 what VCCV capabilities T-PE1 supports. This is the same VCCV
parameter as would be used if T-PE1 and T-PE2 were connected directly
by T-LDP. S-PE2, which is a PW switching point, as part of the
adaptation function for interface parameters, processes locally the
VCCV parameter then passes it to T-PE2. If there were multiple S-PEs
on the path between T-PE1 and T-PE2, each would carry out the same
Hart et al. Expires December 19, 2006 [Page 3]
Internet-Draft Segmented Pseudo Wire VCCV June 2006
processing, passing along the VCCV parameter. The local processing of
the VCCV parameter removes CC Types specified by the originating T-
PE, except PWE3 Control Word that is passed unchanged. For example,
if T-PE1 indicates as supported CC Types both Control Word and Router
Alert then the S-PE removes the Router Alert CC Type, leaving Control
Word unchanged and then passes the modified VCCV parameter to the
next S-PE along the path.
The far end T-PE (T-PE2) receives the VCCV parameter indicating the
Control Word CC Type only if that is supported by the initial T-PE
(T-PE1) and all S-PEs along the PW path.
The method proposed in this document is a variant to the one
described in [PWE3-MS] which is based on defining a new VCCV sub-TLV
in the optional PW switching point TLV. The advantages of the
proposed method are that it limits the processing of the VCCV
messages only to the S-PE/T-PE node which is the target for the
message. All other S-PE nodes in between are not required to inspect
the VCCV CW and are only required to decrement the TTL of the PW
label. Furthermore, it provides a model of operation consistent with
the operation of MPLS LSP Ping and LSP Trace.
2.1. Single Hop VCCV adaptation for end to end verification
2.1.1. Inband VCCV using Control Word
In Figure 1, if T-PE1, S-PE and T-PE2 support Control Word for VCCV,
then as described in section 1 the control plane negotiates the
common use of Control Word for VCCV end to end.
At the S-PE the data path operations include an outer label pop,
inner label swap and new outer label push. Note that there is no
requirement for the S-PE to inspect the CW.
Thus, the end-to-end connectivity of the multi-segment pseudowire can
be verified by:
a) setting the PWE Control Word CC Type in the VCCV parameter sent
by each T-PE,
b) by each S-PE maintaining the Control Word CC Type in the VCCV
parameter, and
c) inner PW label TTL needs to be set to a large enough value to
allow the packet to reach the far end
Hart et al. Expires December 19, 2006 [Page 4]
Internet-Draft Segmented Pseudo Wire VCCV June 2006
d) by the T-PE sending a VCCV packet that will follow the exact same
datapath at each S-PE as that taken by data packets, and that
will be diverted to VCCV control processing at the destination T-
PE.
2.2. Single Hop VCCV adaptation for partial tracing from T-PE
In order to trace part of the multi-segment pseudowire, the TTL of
the PW label may be used to force the VCCV message to 'pop out' at an
intermediate node. When the TTL expires, the S-PE can determine that
the packet is a VCCV packet by checking the control word. If the
control word format matches that specified in [VCCV], the packet
should be diverted to VCCV processing.
In Figure 1, if T-PE1 sends a VCCV message with the TTL of the PW
label equal to 1, the TTL will expire at the S-PE. T-PE1 can thus
verify the first segment of the pseudo wire.
Note that this use of the TTL is subject to the caution expressed in
[VCCV]. If a penultimate LSR between S-PEs or between an S-PE and a
T-PE manipulates the PW label TTL, the VCCV message may not emerge
from the MS-PW at the correct S-PE. It is also a requirement that
each S-PE decrement the PW label TTL correctly.
2.3. VCCV between S-PEs
Assuming that all nodes along an MS-PW support the Control Word CC
Type, VCCV between S-PEs may be accomplished using the PW label TTL
as in section 2.2. In Figure-1, the S-PE may verify the path between
it and T-PE2 by sending a VCCV message with the PW label TTL set to
1. Given a more complex network with multiple S-PEs, an S-PE may
verify the connectivity between it and an S-PE two segments away by
sending a VCCV message with the PW label TTL set to 2.
3. Security Considerations
Same as security concerns described in [VCCV].
4. IANA Considerations
All the values of the CC, CV and channel types are as described in
[VCCV].
5. Acknowledgments
The authors would like to thank Vach Kompella, Kendall Harvey and
Michael Hua for their valuable comments and suggestions.
Hart et al. Expires December 19, 2006 [Page 5]
Internet-Draft Segmented Pseudo Wire VCCV June 2006
References
5.1. Normative References
[VCCV] Nadeau, T., et al."Pseudo Wire Virtual Circuit Connection
Verification (VCCV)", Internet Draft
[PWE3-MS] Martini L., ''Segmented Pseudo Wire'', Internet Draft
5.2. Informative References
Author's Addresses
Neil Hart
Alcatel
600 March Rd
Kanata, ON, Canada. K2K 2E6
Email: neil.hart@alcatel.com
Tiberiu Grigoriu
Alcatel
600 March Rd
Kanata, ON, Canada. K2K 2E6
Email: tiberiu.grigoriu@alcatel.com
Mustapha Aissaoui
Alcatel
600 March Rd
Kanata, ON, Canada. K2K 2E6
Email: mustapha.aissaoui@alcatel.com
Matthew Bocci
Alcatel
Voyager Place, Shoppenhangers Rd
Maidenhead, Berks, UK SL6 2PJ
Email: matthew.bocci@alcatel.co.uk
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
Hart et al. Expires December 19, 2006 [Page 6]
Internet-Draft Segmented Pseudo Wire VCCV June 2006
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Hart et al. Expires December 19, 2006 [Page 7]