T-Ldp Hello Reduction; Tracking A T-Ldp Peer With Bfd - Alcatel-Lucent 7950 SR User Configuration Manual

Label Distribution Protocol

T-LDP hello reduction

This feature implements a new mechanism to suppress the transmission of the Hello messages
following the establishment of a Targeted LDP session between two LDP peers. The Hello
adjacency of the targeted session does not require periodic transmission of Hello messages as in
the case of a link LDP session. In link LDP, one or more peers can be discovered over a given
network IP interface and as such, the periodic transmission of Hello messages is required to
discover new peers in addition to the periodic Keep-Alive message transmission to maintain the
existing LDP sessions. A Targeted LDP session is established to a single peer. Thus, once the
Hello Adjacency is established and the LDP session is brought up over a TCP connection, Keep-
Alive messages are sufficient to maintain the LDP session.
When this feature is enabled, the targeted Hello adjacency is brought up by advertising the Hold-
Time value the user configured in the Hello timeout parameter for the targeted session. The LSR
node will then start advertising an exponentially increasing Hold-Time value in the Hello message
as soon as the targeted LDP session to the peer is up. Each new incremented Hold-Time value is
sent in a number of Hello messages equal to the value of the Hello reduction factor before the next
exponential value is advertised. This provides time for the two peers to settle on the new value.
When the Hold-Time reaches the maximum value of 0xffff (binary 65535), the two peers will stop
sending Hello messages for the lifetime of the targeted LDP session.
Both LDP peers must be configured with this feature to bring gradually their advertised Hold-
Time up to the maximum value. If one of the LDP peers does not, the frequency of the Hello
messages of the targeted Hello adjacency will continue to be governed by the smaller of the two
Hold-Time values. This feature complies to draft-pdutta-mpls-tldp-hello-reduce.

Tracking a T-LDP Peer with BFD

BFD tracking of an LDP session associated with a T-LDP adjacency allows for faster detection of
the liveliness of the session by registering the transport address of a LDP session with a BFD
session.
By enabling BFD for a selected targeted session, the state of that session is tied to the state of the
underneath BFD session between the two nodes. The parameters used for the BFD are set with the
BFD command under the IP interface.
Page 336 7950 SR OS MPLS Configuration Guide