Cisco Catalyst 4500 Series - Information about Bidirectional Forwarding Detection

40-3
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 40 Configuring Bidirection Forwarding Detection
Information About Bidirectional Forwarding Detection
Note For the most accurate platform and hardware restrictions, see the Cisco IOS software release notes for
your software version.
Information About Bidirectional Forwarding Detection
• BFD Operation, page 40-3
• Benefits of Using BFD for Failure Detection, page 40-7
BFD Operation
BFD provides a low-overhead, short-duration method of detecting failures in the forwarding path
between two adjacent switches, including the interfaces, data links, and forwarding planes.
BFD is a detection protocol that you enable at the interface and routing protocol levels. Cisco supports
the BFD asynchronous mode, which depends on the sending of BFD control packets between two
systems to activate and maintain BFD neighbor sessions between switches. Therefore, to create a BFD
session, you must configure BFD on both systems (or BFD peers). Once BFD has been enabled on the
interfaces and at the router level for the appropriate routing protocols, a BFD session is created, BFD
timers are negotiated, and the BFD peers will begin to send BFD control packets to each other at the
negotiated interval.
Cisco supports BFD echo mode. Echo packets are sent by the forwarding engine and are forwarded back
along the same path to perform detection. The BFD session at the other end does not participate in the
actual forwarding of the echo packets. See Configuring BFD Echo Mode, page 40-15 for more
information.
This section includes the following subsections:
• Neighbor Relationships, page 40-3
• BFD Detection of Failures, page 40-4
• BFD Version Interoperability, page 40-5
• BFD Session Limits, page 40-5
• BFD Support for Nonbroadcast Media Interfaces, page 40-5
• BFD Support for Nonstop Forwarding with Stateful Switchover, page 40-5
• BFD Support for Stateful Switchover, page 40-6
• BFD Support for Static Routing, page 40-6
Neighbor Relationships
BFD provides fast BFD peer failure detection times independently of all media types, encapsulations,
topologies, and routing protocols BGP, EIGRP, OSPF, and static routes. By sending rapid failure
detection notices to the routing protocols in the local switch to initiate the routing table recalculation
process, BFD contributes to greatly reduced overall network convergence time. Figure 40-1 shows a
simple network with two switches running OSPF and BFD. When OSPF discovers a neighbor (1) it sends
a request to the local BFD process to initiate a BFD neighbor session with the OSPF neighbor routers
(2). The BFD neighbor session with the OSPF neighbor router is established (3).