Bidirectional Forwarding Detection; Timers - Nokia 7705 SAR-W Series Manual

MPLS Guide
3.4.1.1
Bidirectional Forwarding Detection (BFD) is supported on the 7705 SAR. In the case
of BFD for RSVP-TE, an RSVP-TE enabled link is registered with the BFD state
machine, and if a failure occurs the RSVP-TE interface is taken out of service. The
BFD implementation on the 7705 SAR works on a hop-by-hop basis, and if BFD
detects a link failure, only the two directly connected MPLS nodes are aware of that
failure. If the node that detects the link failure is an LSR node, it generates PATH-
ERR messages to the originators (the LER nodes) of the failing LSPs. If FRR is
configured, the detecting node takes corrective action itself. See
and
3.4.1.1.1
The 7705 SAR supports per-neighbor tracking when RSVP-TE is used over a
broadcast interface in conjunction with BFD. Per-neighbor tracking enables RSVP-
TE to distinguish neighbors from one another when the outgoing interface is a
broadcast interface that is connected to multiple neighbors over a broadcast domain.
If a BFD session toward a specific neighbor on the broadcast domain goes down, the
session failure triggers consecutive actions (for example, an FRR switchover) only
for the LSPs of the affected neighbor.
3.4.1.2
The following timers are implemented to ensure the successful operation of
RSVP-TE:
3HE 18686 AAAB TQZZA

Bidirectional Forwarding Detection

RSVP-TE Fast Reroute (FRR)
RSVP-TE over Broadcast Interface with BFD

Timers

• bypass-resignal-timer — the bypass resignal timer defines the time between the
global reoptimization of all dynamic bypass RSVP-TE LSPs. For more
information, see Bypass Resignal
• hold-timer — the hold timer defines the amount of time before an LSP is brought
up and is in service, which provides protection against unreliable nodes and
links
• resignal-timer — the resignal timer is used in conjunction with the route
optimization process, especially after a reroute has occurred. If the newly
computed path for an LSP has a better metric than the currently recorded hop
list, an attempt is made to resignal that LSP, and if the attempt is successful, a
make-before-break switchover occurs. If the attempt to resignal an LSP fails, the
LSP continues to use the existing path and another resignal attempt is made the
next time the timer expires.
When the resignal timer expires, a trap and syslog message are generated.
Use subject to Terms available at: www.nokia.com
for more information on these topics.
Timer.
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MPLS and RSVP-TE
LSP Redundancy
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