Behavior of Both Peers
When no hello messages are received from a peer within the configured hello interval,
the peer is treated as if communication has been lost.
When a peer determines that communication has been lost, it can reinitiate the sending
of hello messages. In this case, the peer generates a new source instance different than
the one it previously used for communication with its peer.
Related Topics Configuring RSVP-TE Hello Messages to Determine Peer Reachability on page 297•
RSVP-TE Graceful Restart Overview
RSVP-TE graceful restart enables routers to maintain MPLS forwarding state when a
link or node failure occurs. In a link failure, control communication is lost between two
nodes, but the nodes do not lose their control or forwarding state.
A node failure occurs when the LSR has a failure in the RSVP-TE control plane, but not
in the data plane. The LSR maintains its data forwarding state. Traffic can continue to
be forwarded while RSVP-TE restarts and recovers. The graceful restart feature supports
the restoration and resynchronization of RSVP-TE states and MPLS forwarding state
between the restarting router and its RSVP-TE peers during the graceful restart recovery
period.
The RSVP-TE graceful restart feature enables an LSR to gracefully restart, to act as a
graceful restart helper node for a neighboring router that is restarting, or both.
Announcement of the Graceful Restart Capability
LSRs use the RSVP-TE hello mechanism to announce their graceful restart capabilities
to their peer RSVP-TE routers. Both restarting LSRs and helper LSRs include the
restart_cap object in hello requests and hello acks. The restart_cap object specifies both
the graceful restart time and the graceful restart recovery time:
•
restart time—The sum of how long it takes the sender to restart RSVP-TE after a control
plane failure plus how long it takes to reestablish hello communication with the
neighboring RSVP-TE routers.
•
recovery time—The period within which you want neighboring routers to resynchronize
with the sending router’s RSVP-TE state and MPLS forwarding state after the peers
have re-established hello communication. The restarting LSR advertises the configured
or default recovery time only while the graceful restart is in progress. When the LSR is
not currently restarting or when it is incapable of preserving its MPLS forwarding state
during the restart, the LSR advertises a recovery time of zero.
Both the restarting router and neighboring GR helper routers save the restart and recovery
times that they receive from their peers.
Restarting Behavior
When the control plane fails, the LSR stops sending hello messages to its RSVP-TE
neighbors. However, as a restarting router the LSR can continue to forward MPLS traffic
263Copyright © 2010, Juniper Networks, Inc.
Chapter 3: MPLS Overview
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