MPLS Support for Graceful Restart
Many large network deployments use MPLS as an underlying encapsulation technology on top of the Layer 2 frames. While this concept adds some complexity to the design of a GR deployment, it is perfectly doable. Network designers need to look for support for GR protocol extensions among the signaling protocols intended for use with MPLS. For an LDP-based network, support of GR within LDP is necessary. For Resource Reservation Protocol (RSVP)-signaled point to multipoint (P2MP) LSPs, GR must be supported for those LSPs.
Graceful Restart in RSVP
RSVP advertises its ability to support GR protocol extensions during the initial process of establishing adjacencies. The RSVP Hello message contains an additional object, the Restart Capability Object (ResCapObj), which is used to signal both the capability and the desire for GR support.
In addition, ResCapObj contains values for two important timers: the restart timer and the recovery timer. The restart timer advertises how long a neighbor should wait to receive a Hello from the restarting router before it declares it dead. The JUNOS default value is 60 seconds. The recovery timer defines the maximum time allocated for GR support. During this time, all supporting neighbors (helpers) send Path messages to the failed router containing either the Recover Label Object or the list of labels previously advertised by the restarting router.
If the node sends the RSVP Hello message with both restart and recovery timers ...