When BFD support is configured with IS-IS as a registered protocol with BFD, IS-IS receives forwarding path detection failure
messages from BFD. BFD support for IS-IS can be configured in either router address-family configuration mode or interface
configuration mode. IS-IS IPv6 can run in single-topology or in Multi-Topology (MT) mode.
IS-IS BFD supports both IPv4 and IPv6 on the same adjacency for single-topology or multi-topology mode. If BFD is enabled
for both IPv4 and IPv6, IS-IS sends two BFD session creation requests to BFD. For single-topology mode, the IS-IS adjacency
state can only be UP if both BFD sessions are UP. If either of the BFD sessions is DOWN, the associated IS-IS adjacency state
is also DOWN. For MT mode, the IS-IS adjacency state can be UP as long as one of topologies has a BFD session in an UP state.