Nokia 7705 SAR-W Series Manual page 106

MPLS and RSVP-TE
Note: Only link protection is possible in this case because packets matching this ILM record
can either terminate on the neighboring router owning the node SID or can be forwarded to
different next hops of the neighboring router, that is, to different next next-hops of the LSR
providing the protection. The LSR providing the connection does not have context to
distinguish among all possible SR-TE LSPs and therefore can only protect the link to the
neighboring router.
If an adjacency to a neighbor fails, the IGP withdraws the advertisement of the link
TLV information as well as its adjacency SID sub-TLV. However, the LTN or ILM
record of the adjacency SID must be kept in the data path for a sufficient period of
time to allow the ingress LER to compute a new path after the IGP converges. If the
adjacency is restored before the timer expires, the timer is aborted as soon as the
new ILM or LTN records are updated with the new primary and backup NHLFE
information. By default, the ILM/LTN and NHLFE information is kept for a period of
15 s.
The adjacency SID hold timer is configured using the adj-sid-hold command and
activated when the adjacency to the neighbor fails due to the following conditions:
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• If the ILM is for a node SID of a directly connected router, the LFA SPF only
provides link protection. The ILM or LTN record of this node SID points to the
backup NHLFE of this LFA next hop. An SR-TE LSP that transits at an LSR and
that matches the ILM of a neighboring node SID automatically takes advantage
of this protection when enabled.
• If the ILM or LTN record is for an adjacency SID, it is treated as in the case of a
node SID of a directly connected router.
When protecting an adjacency SID, the PLR first tries to select a parallel link to
the node SID of the directly connected neighbor. That is the case when the node
SID is reachable over parallel links. The selection is based on lowest interface
ID. If no parallel links exist, regular LFA/remote LFA algorithms are applied to
find a loopfree path to reach the node SID of the neighbor via other neighbors.
The ILM or LTN for the adjacency SID must point to this backup NHLFE and will
benefit from FRR link protection. As a result, an SR-TE LSP that transits at an
LSR and matches the ILM of a local adjacency SID automatically takes
advantage of this protection when enabled.
• At the ingress LER, the LTN record points to the SR-TE LSP NHLFE, which
points to the NHLFE of the SR shortest path tunnel to the node SID or adjacency
SID of the first hop in the ERO of the SR-TE LSP.The FRR link or node
protection at the ingress LER is inherited directly from the SR shortest path
tunnel.
• the network IP interface went down due to a link or port failure or due to the user
performing a shutdown of the port
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MPLS Guide
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