Label Distribution Protocol
7450 ESS MPLS Guide Page 549
If router A and G have an additional LSP terminating on router G, there would now be two tunnels
both terminating on the same router closest to the final destination. For IGP, it does not make any
difference on the numbers of LDPs to G, only that there is at least one LSP to G. In this case, the
LSP metric will be considered by LDP when deciding which LSP to stitch for the LDP over RSVP
connection.
The IGP only passes endpoint information to LDP. LDP looks up the tunnel table for all tunnels to
that endpoint and picks up the one with the least tunnel metric. There may be many tunnels with
the same least cost. Note that only /32 FEC prefixes will be resolved over RSVP LSPs within an
area.
LDP over RSVP and ECMP
ECMP for LDP over RSVP is supported (also see ECMP Support for LDP on page 535). If ECMP
applies, all LSP endpoints found over the ECMP IGP path will be installed in the routing table by
the IGP for consideration by LDP. It is important to note that IGP costs to each endpoint may
differ because IGP selects the farthest endpoint per ECMP path.
LDP will choose the endpoint that is highest cost in the route entry and will do further tunnel
selection over those endpoints. If there are multiple endpoints with equal highest cost, then LDP
will consider all of them.
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