Bfd Detection Of Failures - Cisco Catalyst 4500 Series Software Configuration Manual

Information About Bidirectional Forwarding Detection
Figure 40-1
172.18.0.1
Figure 40-2
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.
Figure 40-2
172.18.0.1
A routing protocol needs to register with BFD for every neighbor it acquires. Once a neighbor is
registered, BFD initiates a session with the neighbor if a session does not already exist.
OSPF registers with BFD when:
•
•
On broadcast interfaces, OSPF establishes a BFD session only with the designated router (DR) and
backup designated router (BDR), but not between any two switches (routers) in DROTHER state.

BFD Detection of Failures

Once a BFD session has been established and timer negations are complete, BFD peers send BFD control
packets that act in the same manner as an IGP hello protocol to detect liveliness, except at a more
accelerated rate. The following information should be noted:
•
•
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
40-4
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
Tearing Down an OSPF Neighbor Relationship
OSPF
3
BFD
172.16.10.2
Router A
A neighbor finite state machine (FSM) transitions to full state.
Both OSPF BFD and BFD are enabled.
BFD is a forwarding path failure detection protocol. BFD detects a failure, but the routing protocol
must take action to bypass a failed peer.
Typically, BFD can be used at any protocol layer. However, the Cisco implementation of BFD
supports only Layer 3 clients, in particular, the BGP, EIGRP, and OSPF routing protocols, and static
routing.
Chapter 40
1
OSPF neighbors
BFD neighbors
3
172.16.10.1
4
OSPF neighbors
X
BFD neighbors
X
2
1
X
172.16.10.1
Configuring Bidirection Forwarding Detection
OSPF
2
BFD
Router B
172.17.0.1
OSPF
3
BFD
Router B
172.17.0.1