The router supports weighted ECMP in cases where LDP resolves a FEC over an ECMP set of direct next hops corresponding to IP network interfaces, and where it resolves the FEC over an ECMP set of RSVP-TE tunnels. See Weighted Load Balancing for LDP over RSVP for information about LDP over RSVP.
Weighted ECMP for direct IP network interfaces uses a load-balancing-weight configured under the config>router>ldp>interface-parameters>interface context. Similar to LDP over RSVP, Weighted ECMP for LDP is enabled using the weighted-ecmp command under the config>router>ldp context. If the interface becomes an ECMP next hop for an LDP FEC, and all the other ECMP next hops are interfaces with configured (non-zero) load-balancing weights, then the traffic distribution over the ECMP interfaces is proportional to the normalized weight. Then, LDP performs the normalization with a granularity of 64.
If one or more of the LDP interfaces in the ECMP set does not have a configured-load-balancing weight, then the system falls back to ECMP.
If both an IGP shortcut tunnel and a direct next hop exist to resolve a FEC, LDP prefers the tunneled resolution. Therefore, if an ECMP set consists of both IGP shortcuts and direct next hops, LDP only load balances across the IGP shortcuts.
LDP only uses configured LDP interface load balancing weights with non-LDP over RSVP resolutions.
Weights are normalized across all possible next-hops for a FEC. If the number of ECMP routes configured with the configure>router>ldp>max-ecmp-routes is less than the actual number of next-hops, traffic is load-balanced using the normalized weights from the first max-ecmp-routes next-hop. This can cause load distribution within the LDP max-ecmp-routes that is not representative of the distribution that would occur across all ECMP next-hops.