BFD for Layer 3 Protocols

BFD can be configured for use with the following protocols:

BFD must be enabled at the interface and routing protocol levels. BFD asynchronous mode depends on the sending of BFD control packets between two systems to activate and maintain BFD neighbor sessions between routers. Therefore, BFD must be configured on both BFD peers.

A BFD session is created after BFD is enabled on the interfaces and at the router level for the appropriate routing protocols. BFD timers are then negotiated, and the BFD peers begin to send BFD control packets to each other at the negotiated interval.

BFD provides one point of forwarding path monitoring when more than one Layer 3 application wants to monitor a host. BFD runs a session for that host and provides the status to multiple applications, instead of multiple applications running individual sessions to the host.

By sending rapid failure detection notices to the routing protocols in the local device to initiate the routing table recalculation process, BFD contributes to greatly reducing overall network convergence time.

Note

Note

BFD, IS-IS, and OSPF stop operating when Rapid Spanning Tree Protocol (RSTP) path-cost changes are made to the Alt Discarding port on the switch.

The following figure shows the establishment of a BFD session where OSPF discovers a neighbor and sends a request to BFD requesting that a BFD neighbor session be created with the OSPF neighbor router.

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Establishing a BFD neighbor session
  1. OSPF discovers a neighbor.
  2. OSPF requests that the local BFD process initiate a BFD neighbor session with the OSPF neighbor router.
  3. A BFD neighbor session is established with the OSPF neighbor router.

The following figure shows the termination of a BFD neighbor session after a failure occurs in the network.

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Terminating a BFD neighbor session
  1. A network failure occurs.
  2. The BFD session with the OSPF neigbor router is torn down.
  3. BFD notifies the local OSPF process that the BFD neighbor is not reachable.
  4. The local OSPF process tears down the OSPF relationship and starts reconverging.