Label Distribution Protocol
7450 ESS MPLS Guide Page 563
C) If the second set is used, the algorithm selects the tunneled LFA next-hop which endpoint
corresponds to the node advertising the prefix.
→ If more than one tunneled next-hop exists, it selects the one with the lowest LSP
metric.
→ If still more than one tunneled next-hop exists, it selects the one with the lowest
tunnel-id.
→ If none is available, it continues with rest of the tunneled LFAs in second set.
D) Within the selected set, the algorithm splits the LFA next-hops into two sets:
→ The first set consists of LFA next-hops which do not go over the PN used by
primary next-hop.
→ The second set consists of LFA next-hops which go over the PN used by the primary
next-hop.
E) If there is more than one LFA next-hop in the selected set, it will pick the node-protect
type in favor of the link-protect type.
F) If there is more than one LFA next-hop within the selected type, then it will pick one
based on the least total cost for the prefix. For a tunneled next-hop, it means the LSP
metric plus the cost of the LSP endpoint to the destination of the prefix.
G) If there is more than one LFA next-hop within the selected type (ecmp-case) in the first
set, it will select the first direct next-hop from the remaining set. This is not a
deterministic selection and will vary following each SPF calculation.
H) If there is more than one LFA next-hop within the selected type (ecmp-case) in the second
set, it will pick the tunneled next-hop with the lowest cost from the endpoint of the LSP to
the destination prefix. If there remains more than one, it will pick the tunneled next-hop
with the lowest tunnel-id.
Loop-Free Alternate Calculation for Inter-Area/inter-Level Prefixes
When SPF resolves OSPF inter-area prefixes or IS-IS inter-level prefixes, it will compute an LFA
backup next-hop to the same exit area/border router as used by the primary next-hop.
Loop-Free Alternate Shortest Path First (LFA SPF) Policies
To Next Page
Loading...
