Rsvp Graceful Restart Helper - Alcatel-Lucent 7450 Manual

MPLS and RSVP

RSVP Graceful Restart Helper

This gr-helper command enables the RSVP Graceful Restart Helper feature.
The RSVP-TE Graceful Restart helper mode allows the SR OS based system (the helper node) to
provide another router that has requested it (the restarting node) a grace period, during which the
system will continue to use RSVP sessions to neighbors requesting the grace period. This is
typically used when another router is rebooting its control plane but its forwarding plane is
expected to continue to forward traffic based on the previously available Path and Resv states.
The user can enable Graceful Restart helper on each RSVP interface separately. When the GR
helper feature is enabled on an RSVP interface, the node starts inserting a new Restart_Cap Object
in the Hello packets to its neighbor. The restarting node does the same and indicates to the helper
node the desired Restart Time and Recovery Time.
The GR Restart helper consists of a couple of phases. Once it loses Hello communication with its
neighbor, the helper node enters the Restart phase. During this phase, it preserves the state of all
RSVP sessions to its neighbor and waits for a new Hello message.
Once the Hello message is received indicating the restarting node preserved state, the helper node
enters the recovery phase in which it starts refreshing all the sessions that were preserved. The
restarting node will activate all the stale sessions that are refreshed by the helper node. Any Path
state that did not get a Resv message from the restarting node once the Recovery Phase time is
over is considered to have expired and is deleted by the helper node causing the proper Path Tear
generation downstream.
The duration of the restart phase (recovery phase) is equal to the minimum of the neighbor's
advertised Restart Time (Recovery Time) in its last Hello message and the locally configured
value of the max-restart (max-recovery) parameter.
When GR helper is enabled on an RSVP interface, its procedures apply to the state of both P2P
and P2MP RSVP LSP to a neighbor over this interface.
7450 ESS MPLS Guide Page 49