Signaling LDP Label Advertisement Completion
Extracted elements (21)
In LDP Graceful Restart, without End-of-LIB Notification, stale forwarding state must be retained until a configured time period expires. Receiving End-of-LIB allows a speaker to immediately discard stale state from a restarted peer and reclaim resources rather than waiting for timeout.
The End-of-LIB mechanism is applicable only to 'Downstream Unsolicited' advertisement mode. In 'Downstream on Demand' mode, the speaker explicitly requests specific label bindings and already knows when it has received them, making End-of-LIB redundant.
The Unrecognized Notification capability is required because RFC 5036 does not define behavior for an LDP speaker receiving a Notification with an unknown Status Code. Using this capability at session establishment avoids backward-compatibility problems when introducing new Status Codes such as End-of-LIB.
When responding to a Wildcard Label Request, sending an End-of-LIB Notification after completing advertisements for the requested FEC type eliminates uncertainty for the requesting peer about when the full set of bindings has been received.
Without End-of-LIB Notification in LDP-IGP Synchronization scenarios, the speaker must rely on heuristics to determine when all peer label bindings are received, which can cause premature IGP signaling (dropping traffic) or delayed signaling (suboptimal paths). The End-of-LIB Notification makes the synchronization point deterministic.
The End-of-LIB mechanism applies to LDP peers discovered via either basic discovery or extended discovery mechanisms as defined in Section 2.4 of RFC 5036.
There is no guarantee that an LDP speaker will receive or send an End-of-LIB Notification even if the Unrecognized Notification capability has been advertised by both peers, as supporting the capability does not mandate sending or processing End-of-LIB. The EOL timer handles this gap.
An LDP speaker MUST NOT send an End-of-LIB Notification to a peer unless that peer has advertised the Unrecognized Notification capability during session establishment. This applies to peers discovered via both basic and extended discovery mechanisms.
An LDP speaker SHOULD send the End-of-LIB Notification per FEC Type even if it has zero label bindings to advertise to that peer.
An LDP speaker SHOULD signal completion of its label advertisements to a peer via a Notification message if its peer has advertised the Unrecognized Notification capability during session establishment.
An LDP speaker SHOULD start a per-peer EOL Notification timer immediately following LDP session establishment. The default value of 60 seconds is RECOMMENDED, and the value SHOULD be configurable.
If an End-of-LIB Notification message is received after the EOL Notification timer has already expired, the message SHOULD be ignored.
The End-of-LIB Notification message MUST carry a status TLV (with E- and F-bits set to zero) with Status Code 0x0000002F, and a FEC TLV with the Typed Wildcard FEC Element identifying the FEC type for which advertisements are complete.
The U-bit and F-bit in the Unrecognized Notification Capability TLV MUST be 1 and 0, respectively, as required by the LDP Capabilities specification (RFC 5561), and the S-bit MUST be 1 to indicate the capability is being advertised.
The End-of-LIB Notification is a Notification message carrying the End-of-LIB Status Code (0x0000002F) and a FEC TLV with a Typed Wildcard FEC Element, sent by an LDP speaker to signal that it has completed initial label advertisements for a given FEC type following session establishment.
The Unrecognized Notification capability is a Capability Parameter advertised in the LDP Initialization message, signaling that the speaker will ignore Notification messages carrying a non-fatal, unrecognized Status Code rather than treating them as errors.
IANA assigned the 'End-of-LIB' status code 0x0000002F from the LDP Status Code Name Space (IETF Consensus region) defined by RFC 5036.
IANA assigned the 'Unrecognized Notification' capability code point 0x0603 from the LDP TLV Type name space (IETF Consensus region) defined by RFC 5036.
No security considerations beyond those applicable to the base LDP specification (RFC 5036) and the MPLS/GMPLS security framework (RFC 5920) apply to signaling the End-of-LIB condition.
The EOL Notification timer is started immediately following LDP session establishment; it is reset by any subsequent label advertisement from the peer and stopped upon receipt of an End-of-LIB Notification. If the timer expires without receipt of a notification, the speaker behaves as if the End-of-LIB Notification was received.
The Unrecognized Notification Capability TLV is 5 bytes: a 16-bit type field (0x0603) with U-bit=1 and F-bit=0, a 16-bit Length field, and an 8-bit field containing the S-bit (must be 1) and 7 reserved bits.