Alcatel-Lucent 7450 Manual page 145

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Behavior of MPLS Options in Inter-Area LSP
The automatic ABR selection for an inter-area LSP does not change prior implementation inter-
area LSP behavior of many of the LSP and path level options. There is, however, a number of
enhancements introduced by the automatic ABR selection feature as explained in the following.
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7450 ESS MPLS Guide
perform a Global Revertive Make-Before-Break (MBB) to re-optimize the LSP
primary path via the ABR which currently has the best path for the destination prefix
of the LSP.
When the local exit ABR node goes into IS-IS overload or is put into node TE Graceful
Shutdown. In this case, the ingress LER will perform a MBB to re-optimize the LSP
primary path via the ABR which currently has the best path for the destination prefix of
the LSP. The MBB is performed at the receipt of the PathErr message for the node TE
shutdown or at the next timer or manual re-optimization of the LSP path in the case of the
receipt of the IS-IS overload bit.
Features such as path bandwidth reservation and admin-groups continue to operate within
the scope of all areas since they rely on propagating the parameter information in the Path
message across the area boundary.
The TE graceful shutdown and soft pre-emption features will continue to support MBB of
the LSP path to avoid the link or node that originated the PathErr message as long as the
link or node is in the local area of the ingress LER. If the PathErr originated in a remote
area, the ingress LER will not be able to avoid the link or node when it performs the MBB
since it computes the path to the local ABR exit router only. There is, however, an
exception to this for the TE graceful shutdown case only. An enhancement has been added
to cause the upstream ABR nodes in the current path of the LSP to record the link or node
to avoid and will use it in subsequent ERO expansions. This means that if the ingress LER
computes a new MBB path which goes via the same exit ABR router as the current path
and all ABR upstream nodes of the node or link which originated the PathErr message are
also selected in the new MBB path when the ERO is expanded, the new path will indeed
avoid this link or node. The latter is a new behavior introduced with the automatic ABR
selection feature.
The support of MBB to avoid the ABR node when the node is put into TE Graceful
Shutdown is a new behavior introduced with the automatic ABR selection feature.
The use-te-metric option in CSPF cannot be propagated across the area boundary and
thus will operate within the scope of the local area of the ingress LER node. This is a new
behavior introduced with the automatic ABR selection feature.
The srlg option on bypass LSP will continue to operate locally at each PLR within each
area. The PLR node protecting the ABR will check the SRLG constraint for the path of
the bypass within the local area.
The srlg option on secondary path is allowed to operate within the scope of the local area
of the ingress LER node with the automatic ABR selection feature.
MPLS and RSVP
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