Virtual Circuit Connectivity Verification (VCCV) Capability Advertisement for MPLS Transport Profile (MPLS&nbhy;TP)

Proactive Connectivity Verification (CV), Continuity Check (CC), and Remote Defect Indication (RDI) for the MPLS Transport Profile 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 and 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.

BFD: Bidirectional Forwarding Detection CC: Continuity Check CV: Connectivity Verification PE: Provider Edge VCCV: Virtual Circuit Connectivity Verification

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 .

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 . 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.

The format of the VCCV Extended CV Advertisement is a TLV where the format is as follows:

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.

defines coordinated and independent modes of monitoring point-to-point bidirectional connection that can be applied to monitoring PWs. At the same time, 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 Only Fault Detection and Status Signaling Independent Mode 0x01 0x02 Coordinated Mode 0x04 0x08

According to , connectivity verification is part of MPLS-TP CC/CV operation that can be used with VCCV Control Channel Type 1 . 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 selection rules that have been defined in Section 7 of and updated in Section 4 of are augmented in this document. If VCCV Control Channel Type 1 is chosen according to Section 7 of 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: 0x08 - Coordinated mode for PW Fault Detection and AC/PW Fault Status Signaling 0x04 - Coordinated mode for PW Fault Detection only 0x02 - Independent mode for PW Fault Detection and AC/PW Fault Status Signaling 0x01 - Independent mode for PW Fault Detection only

The PW Interface Parameters Sub-TLV registry is defined in . IANA has reserved a new PW Interface Parameters Sub-TLV type as follows: Parameter ID Length Description Reference 0x19 variable VCCV Extended CV Parameter This document

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 of this document. The remaining values (0x10 through 0x80) are to be assigned by IANA using the "IETF Review" policy defined in . 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

Routers that implement the additional CV Type defined herein are subject to the same security considerations as defined in , , , and . This specification does not raise any additional security issues beyond those.

The author gratefully acknowledges the thoughtful review, comments, and explanations provided by Dave Allan and Carlos Pignataro.