Cisco NCS 5500 Series

CHAPTER 9
Implementing Fast Reroute Loop-Free Alternate
Fast Reroute Loop-Free Alternate feature enables you to tunnel a packet around a failed link to a remote
loop-free alternate that is more than one hop away.
• Prerequisites for Fast Reroute with Loop-Free Alternate, on page 249
• Restrictions for Fast Reroute with Loop-Free Alternate, on page 249
• IS-IS and FRR, on page 250
• Repair Paths, on page 250
• LFA Overview, on page 250
• LFA Calculation, on page 251
• Interaction Between RIB and Routing Protocols, on page 251
• Fast Reroute with Remote Loop-Free Alternate, on page 252
• Configuration , on page 253
Prerequisites for Fast Reroute with Loop-Free Alternate
• Fast Reroute with Loop-Free Alternate functionality can protect paths that are reachable through an
interface only if the interface is a point-to-point interface.
• When a LAN interface is physically connected to a single neighbor, you should configure the LAN
interface as a point-to-point interface so that it can be protected through Loop-Free Alternate (LFA) FRR.
• For a proper deployment for Fast Reroute with Remote Loop-Free Alternate feature, the protected link
should also be configured with BFD
Restrictions for Fast Reroute with Loop-Free Alternate
• Load balance support is available for FRR-protected prefixes, but the 50 ms cutover time is not guaranteed.
• A maximum of eight FRR-protected interfaces can simultaneously undergo a cutover.
• LFA calculations are restricted to interfaces or links belonging to the same level or area. Hence, excluding
all neighbors on the same LAN when computing the backup LFA can result in repairs being unavailable
in a subset of topologies.
• Only physical and physical port-channel interfaces and subinterfaces are protected. Tunnels and virtual
interfaces are not protected.
Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x
249