Bypass Resignal Timer - Nokia 7705 SAR-W Series Manual

MPLS and RSVP-TE
Table 6

3.7.2 Bypass Resignal Timer

When the bypass resignal timer is enabled, MPLS makes a request to CSPF for the
best path for each dynamic bypass LSP originated on the node. The constraints of
the first associated LSP primary path that originally triggered the signaling of the
bypass LSP must be satisfied. In order to do this, MPLS saves the original Path State
Block (PSB) of the LSP primary path, even if the path is torn down.
If CSPF returns no path or returns a new path that is equal in cost to the current path,
the PSB associations are not updated. If CSPF returns a new path with a different
cost from the current one, MPLS signals it.
When the new path is successfully signaled, MPLS evaluates each PSB of each PLR
(that is, each unique avoid-node or avoid-link constraint) associated with the older
bypass LSP path to check whether the corresponding LSP primary path constraints
are still satisfied by the new bypass LSP path. If the constraints are satisfied, the PSB
association is moved to the new bypass LSP.
If the constraints are not satisfied, the PSB remains associated with the older bypass
LSP and will be checked at the next background PSB re-evaluation or at the next
timed or manual bypass reoptimization. Additionally, if the older bypass LSP is SRLG
disjoint with a primary path that has the non-strict SRLG condition and the new
bypass LSP is not SRLG disjoint, the PSB association is not moved.
If a PLR associated with a bypass LSP is active, the corresponding PSBs remain
associated with the older bypass LSP until the global revertive make-before-break
(MBB) operation tears down all corresponding primary paths, which also causes the
older bypass LSP to be torn down.
When the bypass resignal timer is configured, a PSB re-evaluation task is initiated
that runs in the background of each RSVP-TE session to determine whether an
existing manual or dynamic bypass is more optimal for that session. If the PSB
re-evaluation task finds a more optimal bypass, it moves the PSB association to it. If
the PLR for this session is active, no action is taken and the PSB is re-examined at
the next re-evaluation.
72
FRR Terminology (Continued)
Term
SRLG disjoint
Use subject to Terms available at: www.nokia.com
Definition
A path is considered to be SRLG disjoint from a given link or
node if the path does not use any links or nodes that belong to
the same SRLG as the given link or node
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