Neighbor Relationships - Cisco Catalyst 4500 Series Configuration Manual

Chapter 37 Configuring Bidirection Forwarding Detection
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
information.
This section includes the following subsections:
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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.
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).
Figure 37-1
172.18.0.1
Figure 37-2
with the OSPF neighbor router is torn down (2). BFD notifies the local OSPF process that the BFD
neighbor is no longer reachable (3). The local OSPF process tears down the OSPF neighbor relationship
(4). If an alternative path is available, the routers will immediately start converging on it.
OL-25340-01
Neighbor Relationships, page 37-3
BFD Detection of Failures, page 37-4
BFD Version Interoperability, page 37-4
BFD Session Limits, page 37-5
BFD Support for Nonbroadcast Media Interfaces, page 37-5
BFD Support for Nonstop Forwarding with Stateful Switchover, page 37-5
BFD Support for Stateful Switchover, page 37-5
BFD Support for Static Routing, page 37-6
Establishing a BFD Neighbor Relationship
OSPF
2
BFD
172.16.10.2
Router A
shows what happens when a failure occurs in the network (1). The BFD neighbor session
Information About Bidirectional Forwarding Detection
Configuring BFD Echo Mode, page 37-14
1
OSPF neighbors
BFD neighbors
3
172.16.10.1
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
for more
Figure 37-1 shows a
OSPF
2
BFD
Router B
172.17.0.1
37-3