Alcatel-Lucent 7950 SR User Configuration Manual page 96

Advanced MPLS/RSVP Features
7. If there is more than 1 ABR that advertized a prefix, CSPF will calculate a path for all
8. The path for an intra-area LSP path will not be able to exit and re-enter the local area of
Rerouting of Inter-Area LSP
In prior implementation, an inter-area LSP path would have been re-routed if a failure or a
topology change occurred in the local or a remote area while the ABR loose-hop in the path
definition was still up. If the exit ABR node went down, went into IS-IS overload, or was put into
node TE graceful shutdown, the LSP path will remain down at the ingress LER.
One new behavior introduced by the automatic selection of ABR is the ability of the ingress LER
to reroute an inter-area LSP primary path via a different ABR in the following situations:
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attempted a path all the way to the last hop in the local area, node E. Instead, CSPF stops
the path at node A which will further expand the ERO by including link D-E as part of the
path in area 0.
ABRs. Only the shortest path will be withheld. If more than one path has the shortest path,
CSPF will pick a path randomly or based on the least-fill criterion if enabled. If more than
one ABR satisfies the least-fill criterion, CSPF will also pick one path randomly.
the ingress LER. This behavior was possible in prior implementation when the user
specified a loose hop outside of the local area or when the only available path was via TE
links outside of the local area.
When the local exit ABR node fails, There are two cases to consider:
 The primary path is not protected at the ABR and is thus torn down by the previous
hop in the path. In this case the ingress LER will retry the LSP primary path via the
ABR which currently has the best path for the destination prefix of the LSP.
 The primary path is protected at the ABR with a manual or dynamic bypass LSP. In
this case the ingress LER will receive a Path Error message with a notification of a
protection becoming active downstream and a RESV with a 'Local-Protection-In-
7950 SR OS MPLS Configuration Guide