The Open Shortest Path First version 2 (OSPFv2) Loop-Free Alternate Fast Reroute feature is used to reroute traffic if a link fails. Repair paths are calculated and stored in the Routing Information Base (RIB). When a primary path fails, the repair path is used without requiring route recomputation. OSPFv2 Loop-Free Alternate Fast Reroute is not supported on virtual links, but it is supported on VPN routing and forwarding (VRF) OSPF instances. You can configure a traffic engineering (TE) tunnel interface as a repair path but not as a protected interface.
The srlg attribute is considered first in the calculation of a repair path. A shared risk link group (SRLG) is a group of next-hop interfaces that are likely to fail simultaneously. You can issue the srlg command to assign an interface to an SRLG.
The primary path attribute is considered second. You can configure the primary path attribute so that a particular repair path is used.
The interface-disjoint attribute is considered third. You can set the interface-disjoint attribute to prevent selection of pointtopoint interfaces, which have no alternate next hop for rerouting.
The lowest metric attribute is considered fourth. The lowest cost route might not be the most stable route. However, you can configure the metric attribute to ensure that routes with lower metrics are selected as repair paths.
The linecard-disjoint attribute is considered fifth. Interfaces on the same line card are likely to fail at the same time if there is a problem with the card.
The node-protecting attribute is considered sixth. You can configure the node-protecting attribute so that the primarypath gateway router is not selected for the repair path.
The broadcast-interface-disjoint attribute is considered last. You can configure the broadcast-interface-disjoint attribute so that the repair path does not use the broadcast network to which the primary path is connected.