Only LDP FRR is supported. LDP FRR uses the LFA computed for IP prefixes to determine the backup path to use for LDP FEC that are installed in the MPLS tables. This section is here only for completeness of description for this feature.
This feature provides for the use of the Loop-Free Alternate (LFA) backup next-hop for forwarding in-transit and CPM generated IP packets when the primary next-hop is not available. This means that a node resumes forwarding IP packets to a destination prefix without waiting for the routing convergence.
When any of the following events occurs, IGP instructs in the fast path the IOM, the forwarding engine to enable the LFA backup next-hop:
OSPF/IS-IS interface goes operationally down: physical or local admin shutdown.
Timeout of a BFD session to a next-hop when BFD is enabled on the OSPF/IS-IS interface.
IP FRR is supported on IPv4 and IPv6 OSPF/IS-IS prefixes forwarded in the base router instance to a network IP interface or to an IES SAP interface or spoke interface. It is also supported for VPRN VPN-IPv4 OSPF prefixes and VPN-IPv6 OSPF prefixes forwarded to a VPRN SAP interface or spoke interface.
The LFA next-hop precomputation by IGP is described in RFC 5286, Basic Specification for IP Fast Reroute: Loop-Free Alternates.