RFC7189
Internet Engineering Task Force (IETF) G. Mirsky Request for Comments: 7189 Ericsson Category: Standards Track March 2014 ISSN: 2070-1721
Virtual Circuit Connectivity Verification (VCCV) Capability Advertisement for MPLS Transport Profile (MPLS-TP)
Abstract
This document specifies how signaling and selection processes for Pseudowire (PW) Virtual Circuit Connectivity Verification (VCCV) are modified to ensure backward compatibility and allow use of proactive Connectivity Verification (CV), Continuity Check (CC), and Remote Defect Indication (RDI) over MPLS Transport Profile (MPLS-TP) PWs. This document introduces four new CV types and, to accommodate them, a new VCCV Extended CV parameter for PW Interface Parameters Sub-TLV is defined.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7189.
Copyright Notice
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Contents
Introduction
Proactive Connectivity Verification (CV), Continuity Check (CC), and Remote Defect Indication (RDI) for the MPLS Transport Profile RFC6428 are applicable to all constructs of the MPLS-TP, including pseudowires (PWs). If the control plane is used to operate and manage PWs then the procedures defined in RFC5085 and RFC5885 should be used to select the proper type of Control Channel and the corresponding type of Connectivity Verification. This document specifies how signaling and selection processes are modified to ensure backward compatibility and allow use of proactive CV-CC-RDI over MPLS-TP PWs.
Conventions Used in This Document
Terminology
BFD: Bidirectional Forwarding Detection
CC: Continuity Check
CV: Connectivity Verification
PE: Provider Edge
VCCV: Virtual Circuit Connectivity Verification
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119.
MPLS-TP CC-CV on Pseudowires
PW VCCV can support several CV Types, and it can support an arbitrary combination of CV modes advertised in the CV Types field of the VCCV Interface Parameter sub-TLV RFC4446 RFC4447. Currently, six types of CV have been defined for PW VCCV. This document introduces four new CV types and, to accommodate them, a new VCCV Extended CV parameter for the PW Interface Parameters Sub-TLV is defined.
VCCV Extended CV Advertisement Sub-TLV
The format of the VCCV Extended CV Advertisement is a TLV where the format is as follows:
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 = 0x19 | Length | CV Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: VCCV Extended CV Parameter Format
The Length field is the length of the sub-TLV, including type and the Length field itself. The minimum length is 4. It is recommended that extensions to the sub-TLV be done in 4-byte increments.
The Reserved field MUST be set to zeroes on transmit and ignored on receive.
The CV Type field is a bitmask that lists types of CV monitoring that a PE is capable of supporting. The VCCV Extended CV parameter sub- TLV MUST appear in combination with the VCCV parameter sub-TLV. If the VCCV parameter sub-TLV is missing, then the VCCV Extended CV parameter sub-TLV SHOULD be ignored.
MPLS-TP CC-CV Types
RFC6428 defines coordinated and independent modes of monitoring point-to-point bidirectional connection that can be applied to monitoring PWs. At the same time, RFC6310 defines how BFD-based
Operations, Administration, and Maintenance (OAM) can map to the status of an Attachment Circuit. Thus, there could be four MPLS-TP CV types for each combination of mode and functionality:
+----------------+-------------------+------------------------------+ | Modes | Fault Detection | Fault Detection and Status | | | Only | Signaling | +----------------+-------------------+------------------------------+ | Independent | 0x01 | 0x02 | | Mode | | | | Coordinated | 0x04 | 0x08 | | Mode | | | +----------------+-------------------+------------------------------+
Table 1: Bitmask Values for MPLS-TP CV Types
MPLS-TP CC-CV Type Operation
According to RFC6428, connectivity verification is part of MPLS-TP CC/CV operation that can be used with VCCV Control Channel Type 1 RFC5085. If VCCV Control Channel Type 1 is selected, then PEs MAY select one of the MPLS-TP CC-CV types as the VCCV CV mechanism to be used for this PW.
CV Type Selection
CV selection rules that have been defined in Section 7 of RFC5085 and updated in Section 4 of RFC5885 are augmented in this document.
If VCCV Control Channel Type 1 is chosen according to Section 7 of RFC5085 and a common set of proactive CV types that are advertised by both PEs includes MPLS-TP CC-CV types and some BFD CV types, then MPLS-TP CC-CV takes precedence over any type of BFD CV. If multiple MPLS-TP CV types are advertised by both PEs, then the following list (ordered by descending priority) is used:
1. 0x08 - Coordinated mode for PW Fault Detection and AC/PW Fault
Status Signaling
2. 0x04 - Coordinated mode for PW Fault Detection only
3. 0x02 - Independent mode for PW Fault Detection and AC/PW Fault
Status Signaling
4. 0x01 - Independent mode for PW Fault Detection only
IANA Considerations
The PW Interface Parameters Sub-TLV registry is defined in RFC4446.
IANA has reserved a new PW Interface Parameters Sub-TLV type as follows:
+-----------+----------+----------------------------+---------------+ | Parameter | Length | Description | Reference | | ID | | | | +-----------+----------+----------------------------+---------------+ | 0x19 | variable | VCCV Extended CV Parameter | This document | +-----------+----------+----------------------------+---------------+
Table 2: New PW Interface Parameters Sub-TLV
VCCV Extended CV Types
IANA has set up a registry of VCCV Extended CV Types. These are 8-bit values. Extended CV Type values 0x01, 0x02, 0x04, and 0x08 are specified in Section 2.2 of this document. The remaining values (0x10 through 0x80) are to be assigned by IANA using the "IETF Review" policy defined in RFC5226. A VCCV Extended Connectivity Verification Type description and a reference to an RFC approved by the IESG are required for any assignment from this registry.
+--------------+----------------------------------------------------+ | Bit(Value) | Description | +--------------+----------------------------------------------------+ | Bit 0 (0x01) | Independent mode for PW Fault Detection only | | Bit 1 (0x02) | Independent mode for PW Fault Detection and AC/PW | | | Fault Status Signaling | | Bit 2 (0x04) | Coordinated mode for PW Fault Detection only | | Bit 3 (0x08) | Coordinated mode for PW Fault Detection and AC/PW | | | Fault Status Signaling | | Bit 4 (0x10) | Unassigned | | Bit 5 (0x20) | Unassigned | | Bit 6 (0x40) | Unassigned | | Bit 7 (0x80) | Unassigned | +--------------+----------------------------------------------------+
Table 3: VCCV Extended Connectivity Verification (CV) Types
Security Considerations
Routers that implement the additional CV Type defined herein are subject to the same security considerations as defined in RFC5085, RFC5880, RFC5881, and RFC6428. This specification does not raise any additional security issues beyond those.
Acknowledgements
The author gratefully acknowledges the thoughtful review, comments, and explanations provided by Dave Allan and Carlos Pignataro.
References
Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC4446 Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
RFC4447 Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
RFC5085 Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
RFC5880 Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
RFC5881 Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June 2010.
RFC5885 Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", RFC 5885, June 2010.
RFC6310 Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations,
Administration, and Maintenance (OAM) Message Mapping",
RFC 6310, July 2011.
RFC6428 Allan, D., Swallow Ed. , G., and J. Drake Ed. , "Proactive
Connectivity Verification, Continuity Check, and Remote
Defect Indication for the MPLS Transport Profile", RFC
6428, November 2011.
Informative References
RFC5226 Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
Author's Address
Greg Mirsky Ericsson
EMail: [email protected]
