Internet DRAFT - draft-ietf-pwe3-mpls-tp-ms-pw
draft-ietf-pwe3-mpls-tp-ms-pw
Network Working Group Siva Sivabalan
INTERNET-DRAFT Sami Boutros
Intended Status: Informational Luca Martini
Cisco Systems
Expires: April 23, 2013 October 20, 2012
Stitching Procedures for Static PW in MPLS-TP Environment
draft-ietf-pwe3-mpls-tp-ms-pw-01.txt
Abstract
The existing procedures for concatenating static and dynamic
pseudowires (PWs) do not take into account the PW status Operation,
Administration, and Maintenance (OAM) messages defined for static PW.
Also, these procedures do not take into account operator functions
such Lock Instruct and Loopback introduced as part of MPLS Transport
Profile (MPLS-TP). This informational document reiterates stitching
procedures for static PW taking into account all the new proposed
extensions.
This document is a product of a joint Internet Engineering Task
Force(IETF) / International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and PWE3 architectures to support the
capabilities and functionalities of a packet transport network.
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
Sivabalan Expires April 23, 2013 [Page 1]
INTERNET DRAFT mpls-tp-ms-pw October 20, 2012
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright and License Notice
Copyright (c) 2012 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. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Lock Operation . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Locking MPLS-TP LSP . . . . . . . . . . . . . . . . . . 4
3.1.1.1. LI originated at T-PE . . . . . . . . . . . . . . . 4
3.1.1.2. LI originated at S-PE . . . . . . . . . . . . . . . 5
3.1.2. Locking PW . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2.1. LI originated at T-PE . . . . . . . . . . . . . . . 5
3.2. Loopback Operation . . . . . . . . . . . . . . . . . . . . 6
3.3. Switching Point PE TLV . . . . . . . . . . . . . . . . . . 6
3.4. VCCV Procedures . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
6. Author's Addresses . . . . . . . . . . . . . . . . . . . . . . 7
Sivabalan Expires April 23, 2013 [Page 2]
INTERNET DRAFT mpls-tp-ms-pw October 20, 2012
1. Introduction
The PWE3 Architecture in [1] defines signaling and encapsulation
techniques for establishing Single Segment PW (SS-PW) between a pair
of terminating PEs. Procedures for stitching two or more static or
dynamic SS-PWs to form Multi-Segment PW (MS-PW) are described in
[2].
These procedures make use of PW status messages carried in LDP TLV
over dynamic PW established via LDP. [3] defines a new PW status OAM
message used to carry PW status in-band over static PW. This message
makes it possible to exchange PW status end-to-end over a MS-PW
consisting of one or more static PW.
[5] specifies operator new Operation, Administration, and Maintenance
(OAM) functions Lock Instruct (LI) and Loopback (LB) for associated
bi-directional circuits such as MPLS-TP LSP, SS-PW, and MS-PW in an
MPLS Transport Profile (MPLS-TP) environment. These functions enable
network operators to lock a circuit (LSP and PW) and operate it in
loopback mode for testing/management purpose.
This informational document describes the application of the existing
PW stitching procedures taking into consideration LI, LB, as well as
PW status OAM messages.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and PWE3 architectures to support the
capabilities and functionalities of a packet transport network.
2. Terminology
LDP: Label Distribution Protocol. MEP: Maintenance End Point.
MIP: Maintenance Intermediate Point. MPLS: Multi Protocol Label
Switching. MPLS-TP: MPLS Transport Profile. MS-PW: Multi-
Segment PseudoWire. LB: Loopback. LI: Lock Instruct. LSP:
Label Switched Path. OAM: MPLS Operations, Administration and
Maintenance. PE: Provide Edge Node. PW: PseudoWire. S-PE:
Switching Provider Edge Node of a MS-PW. SS-PW: Single-Segment
PseudoWire. TLV: Type, Length, and Value. T-PE: Terminating
Provider Edge Node of a MS-PW.
3. Operation
In this section, we explain the use of LI/LB mechanisms referring
to the MS-PW model shown in Figure 1. The SS-PW segments PW1 and PW2
can be either static or dynamic. We assume that PWs are carried over
Sivabalan Expires April 23, 2013 [Page 3]
INTERNET DRAFT mpls-tp-ms-pw October 20, 2012
MPLS-TP LSPs (transport LSPs) so that LI/LB mechanisms can be applied
at the transport LSP level, as well we consider the application of
LI/LB at PW level.
PW status is sent via LDP message and PW OAM message respectively
over dynamic and static PW segments. Note that even though only two
PW segments are considered in the examples below, the described
procedures are applicable to MS-PWs with more than two segments.
+-------+ (PW1) +-------+ (PW2) +-------+
| |------------->| |-------------->| |
| T-PE1 | | S-PE | | T-PE2 |
| |<-------------| |<--------------| |
+-------+ +-------+ +-------+
Figure 1. Reference Model for LI/LB Mechanism
3.1. Lock Operation
3.1.1. Locking MPLS-TP LSP
An MPLS-TP LSP can be taken out of service for maintenance operation
using the LI mechanism described in [5]. LI messages are exchanged
between MPLS-TP Maintenance End Points (MEPs). In the case of MS-PW,
each MPLS-TP LSP associated with a given PW segment can be
individually locked for management purpose. This means that, in a MS-
PW scenario, a T-PE is always a MEP and an S-PE is a MEP for an MPLS-
TP LSP carrying PW segments.
3.1.1.1. LI originated at T-PE
Assume that T-PE1 originates an LI request for the MPLS-TP LSP
carrying PW1. The intended recipient of the message will be the S-PE.
Before locking the MPLS-TP LSP, PW1 and all other PWs associated with
the MPLS-TP LSP will be taken out of service. This means that PW1 and
all other impacted PWs will no longer carry user data.
When S-PE receives an LI request, before locking the MPLS-TP LSP, the
S-PE finds all PWs associated with this MPLS-TP LSP and first sends
the PW status code 0x00000018 (Local PSN-facing PW Receive/Transmit
Faults) on all stitched PWs segments to T-PE2. PW status code is sent
over PW OAM message or LDP message depending on whether the segment
PW2 is static or dynamic.
When T-PE2 receives the PW status codes, it processes them as
described in [3] or [4] depending on whether PW2 is dynamic or
static.
Sivabalan Expires April 23, 2013 [Page 4]
INTERNET DRAFT mpls-tp-ms-pw October 20, 2012
If PW2 is a dynamic segment and does not support PW status, S-PE
needs to withdraw its labels from T-PE2 before locking the MPLS LSP.
For better scalability, S-PE may use the notion of group ID described
in [6] to send PW status or withdraw labels all impacted dynamic PWs
between itself and T-PE2. Use of group ID with PW status OAM over
static PW is TBD.
3.1.1.2. LI originated at S-PE
Let's assume that an operator wants to originate an LI request at S-
PE for the MPLS-TP LSP carrying PW1. The intended recipient of the LI
request is T-PE1. First, S-PE sends PW status code 0x00000018 (Local
PSN-facing PW Receive/Transmit Fault) for PW1 as well as all other
PWs pinned down to MPLS-TP LSP in question to T-PE1 and PW2 and all
other stitched PWs other segments to T-PE2. PW status code is sent
over PW OAM message or LDP message depending on whether the segment
PW2 is static or dynamic. When T-PE2 receives the PW status codes, it
processes them as described in [3] or [4] respectively depending on
whether PW2 is dynamic or static. It then sends LI request message to
T-PE1, and PW1 is no longer used for carrying regular user data.
If PW2 is a dynamic segment and PW status, S-PE needs to withdraw its
labels from T-PE1 and T-PE2 before sending LI request to T-PE1.
For better scalability, S-PE may use the notion of group ID described
in [6] to send PW status or withdraw labels all impacted dynamic PWs.
Use of group ID with PW status OAM over static PW is TBD.
3.1.2. Locking PW
A given PW can also be taken out of service for maintenance operation
without impacting services over other PWs using the LI mechanism
described in [5].
3.1.2.1. LI originated at T-PE
In our example, let's assume that, T-PE1 sends an LI request message
to lock PW1. S-PE is the intended recipient (based on the TTL value
of the PW label). S-PE sends a PW status message with the status code
0x00000018 (Local PSN-facing PW Receive/Transmit Fault) over PW2 to
T-PE2, and locks PW1. PW status code is sent over PW OAM message or
LDP message depending on whether the segment PW2 is static or
dynamic. When T-PE2 receives the PW status codes, it processes them
as described in [3] or [4] depending on whether PW2 is dynamic or
static.
Sivabalan Expires April 23, 2013 [Page 5]
INTERNET DRAFT mpls-tp-ms-pw October 20, 2012
3.2. Loopback Operation
As described in [5], an MPLS-TP LSP or a PW can be setup to in
loopback mode for management purpose, e.g., to test or verify
connectivity of the LSP/PW up to a specific node on the path of the
MPLS-TP tunnel/PW, and to test the LSP/PW performance with respect to
delay/jitter, etc. But, prior to operating in loopback mode, an MPLS-
TP LSP or PW must be successfully locked.
3.3. Switching Point PE TLV
Switching Point PE TLV (S-PE TLV) is used to record information about
S-PE(s) that a PW traverses. An S-PE TLV contains many sub-TLVs as
described in [3]. One such sub-TLV carries the FEC of the last
traversed PW segment.
In the case of MS-PW containing static PW segment(s), if the last
traversed PW segment is statically provisioned, a new sub-TLV
containing the FEC defined for static PW in [7] can be used to
represent the last traversed PW segment. The new sub-TLV type will be
defined in [4].
3.4. VCCV Procedures
The same procedures defined in [3] can be used.
4. Security Considerations
This document does not introduce any additional security
constraints.
5. References
5.1. Normative References
[1] Bradner. S, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March, 1997.
6.2. Informative References
[2] Stewart Bryant, et. al, "Pseudowire Emulation Edge-to-Edge
(PWE3) Architecture", RFC3985, March 2005.
[3] Luca Martini, et. al, "Segmented Pseudowire", draft-ietf-pwe3-
segmented-pw-15.txt (work in progress), June 2010.
[4] Luca Martini, et. al, "Pseudowire Status for Static
Pseudowires", draft-ietf-pwe3-static-pw-status-00.txt (work in
Sivabalan Expires April 23, 2013 [Page 6]
INTERNET DRAFT mpls-tp-ms-pw October 20, 2012
progress), February 2010.
[5] Sami Boutros, et. al, "MPLS Transport Profile Lock Instruct and
Loopback Functions", draft-ietf-mpls-tp-li-lb-00.txt (work in
progress), June 2010.
[6] Luca Martini, et. al, "Pseudowire Setup and Maintenance Using
Label Distribution Protocol (LDP)", RFC4447, April 2006.
[7] Nitin Bahadur, et. al, "LSP-Ping extensions for MPLS-TP",
draft-ietf-mpls-tp-lsp-ping-extensions-01.txt (work in
progress), February 2010.
6. 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
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
United States
Email: lmartini@cisco.com
Sivabalan Expires April 23, 2013 [Page 7]
