Graceful Restart: Figure
This figure illustrates how RSVP graceful restart handles a node failure condition.
Figure 9: Node Failure with RSVP
RSVP graceful restart requires the use of RSVP hello messages. Hello messages are used between RSVP
neighbors. Each neighbor can autonomously issue a hello message containing a hello request object. A receiver
that supports the hello extension replies with a hello message containing a hello acknowledgment (ACK)
object. This means that a hello message contains either a hello Request or a hello ACK object. These two
objects have the same format.
The restart cap object indicates a node’s restart capabilities. It is carried in hello messages if the sending node
supports state recovery. The restart cap object has the following two fields:
Restart Time
Time after a loss in Hello messages within which RSVP hello session can be reestablished. It is possible
for a user to manually configure the Restart Time.
Recovery Time
Time that the sender waits for the recipient to re-synchronize states after the re-establishment of hello
messages. This value is computed and advertised based on number of states that existed before the fault
occurred.
For graceful restart, the hello messages are sent with an IP Time to Live (TTL) of 64. This is because the
destination of the hello messages can be multiple hops away. If graceful restart is enabled, hello messages
(containing the restart cap object) are send to an RSVP neighbor when RSVP states are shared with that
neighbor.
Restart cap objects are sent to an RSVP neighbor when RSVP states are shared with that neighbor. If the
neighbor replies with hello messages containing the restart cap object, the neighbor is considered to be graceful
restart capable. If the neighbor does not reply with hello messages or replies with hello messages that do not
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
116
Implementing RSVP for MPLS-TE and MPLS O-UNI
Graceful Restart
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