To enable CBF+ECMP for SR-ISIS over RSVP-TE:
Configure the resolution of SR over RSVP-TE LSPs as IGP shortcuts.
Configure class based forwarding parameters in the MPLS context (a class forwarding policy, forwarding classes to sets associations, and RSVP-TE LSPs to forwarding sets associations).
Enable class forwarding in the segment routing context.
When SR-ISIS resolves to an ECMP set of RSVP-TE LSPs and class forwarding is enabled in the segment routing context, the following behaviors apply:
If no LSP in the full ECMP set, has been assigned with a class forwarding policy configuration, the set is considered as inconsistent from a CBF perspective. The system programs, in the forwarding path, the whole ECMP set and regular ECMP spraying occurs over the full set.
If the ECMP set refers to more than one class forwarding policy, the set is inconsistent from a CBF perspective. The system programs, in the forwarding path, the whole ECMP set without any CBF information, and regular ECMP spraying occurs over the full set.
In all other cases the ECMP set is considered consistent from a CBF perspective and the following rules apply:
If there is no default set (either user-defined or implicit) referenced in a CBF-consistent ECMP set, the system automatically selects one set as the default one. The selected set is the non-empty one with the lowest ID amongst those referenced by the LSPs of the ECMP set.
The system programs the data-path such that a packet which has been classified to a particular forwarding class is forwarded using the LSPs associated with the forwarding set which itself is associated with that forwarding class. In the event where the forwarding set is composed of multiple LSPs, the system performs ECMP over these LSPs.
Forwarding classes which are either not explicitly mapped to a set or which are mapped to a set for which all LSPs are down are forwarded using the default-set. The system re-elects a default set in cases where all the LSPs of the current default-set become inactive. The system also adapts (updates data-path programming) to configuration or state changes.
The CBF capability is available with any system profile. The number of sets is limited to four with system profile None or A, and to six with system profile B.