Alcatel-Lucent 7450 Manual page 229

MPLS and RSVP
bypass-resignal-timer
Syntax bypass-resignal-timer minutes
no bypass-resignal-timer
Context config>router>mpls
Description
This command triggers the periodic global re-optimization of all dynamic bypass LSP paths
associated with RSVP P2P LSP. The operation is performed at each expiry of the user configurable
bypass LSP re-signal timer.
When this command is enabled, MPLS makes a request to CSPF for the best path for each dynamic
bypass LSP originated on this node. The constraints of the first associated LSP primary path and
which 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 that LSP primary path even if the latter is torn
down.
If CSPF returns no path or returns a new path that is equal in terms of 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 will signal it.
Once the new path is successfully signaled, MPLS will evaluate each PSB of each PLR (i.e., each
unique avoid-node or avoid-link constraint) associated with the older bypass LSP path to check if the
corresponding LSP primary path constraints are still satisfied by the new bypass LSP path. If so, the
PSB association is moved to the new bypass LSP.
Each PSB whose constraints are not satisfied remains associated with the older bypass LSP and will
be checked at the next background PSB re-evaluation, or at the next timer or manual bypass re-
optimization. Furthermore, if the older bypass LSP is SRLG disjoint with a primary path that has the
non-strict SRLG constraint while the new bypass LSP is not SRLG disjoint, the PSB association is
not moved.
If a specific 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) tears down all
corresponding primary paths, which will also cause the older bypass LSP to be torn down.
This feature also implements a background PSB re-evaluation task which audits in the background
each RSVP session and determines if an existing manual or dynamic bypass is more optimal for that
session. If so, it moves the PSB association to this bypass. If the PLR for this session is active, no
action is taken and the PSB will be re-examined at the next re-evaluation.
The periodic bypass re-optimization feature evaluates only the PSBs of the PLRs associated with that
bypass LSP and only against the new bypass LSP path. The background re-evaluation task will,
however, audit all PSBs on the system against all existing manual and dynamic bypass LSPs.
Furthermore, PSBs that have not been moved by the dynamic or manual re-optimization of a bypass
LSP, due to the PSB constraints not being met by the new signaled bypass LSP path, will be re-
evaluated by the background task against all existing manual and dynamic bypass LSPs.
Finally, the background re-evaluation task will check for PSBs that have requested node-protect
bypass LSP but are currently associated with a link-protect bypass LSP, as well as PSBs that
requested FRR protection and that have no association. This is in addition to the attempt made at the
receipt of a Resv on the protected LSP path such that the association is speed up.
This feature is not supported with inter-area dynamic bypass LSP and bypass LSP protecting S2L
paths of a P2MP LSP.
7450 ESS MPLS Guide Page 229