To configure LDP FRR, LFA calculation by the SPF algorithm must first be enabled under the OSPF or IS-IS protocol level with the command:
config>router>ospf>loopfree-alternates
or
config>router>ospf3>loopfree-alternates
or
config>router>isis>loopfree-alternates
Next, LDP must be enabled to use the LFA next hop with the command config>router>ldp>fast-reroute.
If IGP shortcuts are used, they must be enabled under the OSPF or IS-IS routing protocol. As well, they must be enabled under the MPLS LSP context, using the command config>router>mpls>lsp>igp-shortcut.
For information about LFA and IGP shortcut support for OSPF and IS-IS, see the 7705 SAR Routing Protocols Guide, ‟LDP and IP Fast Reroute for OSPF Prefixes” and ‟LDP and IP Fast Reroute for IS-IS Prefixes”.
Both LDP FRR and IP FRR are supported; for information about IP FRR, see the 7705 SAR Router Configuration Guide, ‟IP Fast Reroute (FRR)”.