LDP 'Typed Wildcard' Forwarding Equivalence Class (FEC) for PWid and Generalized PWid FEC Elements
Extracted elements (16)
A PW consistency check is enabled by having LSR A mark all learned Generalized PWid bindings from LSR B as stale, send a Typed Wildcard Label Request (PW type 0x7FFF), and then purge any still-stale bindings upon receipt of the End-of-LIB notification (RFC 5919) from LSR B, leveraging the wildcard to avoid per-PW request messages.
Graceful PW shutdown without a session flap is achieved by sending a single Label Withdraw message containing Typed Wildcard FEC Elements for both PWid and Generalized PWid (PW type 0x7FFF each), causing the peer to delete all corresponding bindings and respond with Label Release messages.
Sending a single PW Status LDP Notification with a Typed Wildcard PW FEC replaces per-PW status notification messages during global failures, which has significant scalability benefits in large networks with many pseudowires.
The Typed Wildcard FEC approach provides a more generalized solution than the existing 'Group ID' field (PWid) and 'PW Grouping ID TLV' (Generalized PWid) mechanisms because it additionally enables Typed Wildcard Label Request messages and allows Label TLVs to further constrain the wildcard to FECs bound to a specific label.
Using a Typed Wildcard PW FEC in an LDP Address Withdraw message allows a PE to withdraw MAC addresses for all VPLS instances (or all instances of a given PW type) in a single message, avoiding the per-VPLS-instance Address Withdraw messages otherwise required by RFC 4762 procedures.
Processing procedures for Typed Wildcard PWid and Generalized PWid FEC Elements are identical to those specified in RFC 5918 for any Typed Wildcard FEC Element type; no new processing logic is introduced by this document.
The general Typed Wildcard FEC mechanism (RFC 5918) requires that a Typed Wildcard FEC Element be individually defined for each FEC Element type; this document fulfills that requirement for the PWid (0x80) and Generalized PWid (0x81) FEC types defined in RFC 4447.
If a 'PW Grouping ID TLV' is received in the same message as a Typed Wildcard FEC for Generalized PWid, the receiving LSR MUST ignore this TLV silently and process the rest of the message.
The PW type field in the Typed Wildcard FEC Element MUST be set to the 'Wildcard' type (0x7FFF) when the wildcard operation is intended to apply to pseudowires of all types.
The Reserved (R) bit in the Typed Wildcard FEC Element MUST be set to ZERO on transmit and ignored on receipt.
When a Typed Wildcard PW FEC Element is used in an LDP Address Withdraw message for VPLS MAC address withdrawal, the MAC List TLV MUST contain an empty list.
When the Typed Wildcard FEC for the Generalized PWid FEC Element is in use, the 'PW Grouping ID TLV' MUST NOT be present in the same LDP message, as these two wildcard mechanisms are mutually exclusive.
The PWid Typed Wildcard FEC Element uses FEC type 0x80 and the Generalized PWid Typed Wildcard FEC Element uses type 0x81, as originally defined in RFC 4447. The 15-bit PW type field scopes the wildcard to a specific PW type or to all types via the 0x7FFF wildcard value.
The Typed Wildcard PW FEC Element may be used in any LDP message that specifies a FEC TLV as a mandatory or optional parameter, including label messages, Notification messages conveying PW Status, and Address Withdraw messages for VPLS MAC withdrawal.
This document introduces no new security considerations beyond those already applicable to RFC 5036 (LDP), RFC 4447 (PW setup), RFC 4762 (VPLS), RFC 5918 (Typed Wildcard FEC), and RFC 5920 (MPLS/GMPLS security framework).
The Typed Wildcard FEC Element for PWid and Generalized PWid is encoded as: Typed Wcard field (1 octet, value 0x05), Type field (1 octet, 0x80 for PWid or 0x81 for Generalized PWid), Len field (1 octet, value 2), followed by a reserved R bit and a 15-bit PW type field, totaling 5 octets.