Cisco ME 3400 Software Configuration Manual page 799

Chapter 35 Configuring IP Unicast Routing
Figure 35-6
172.18.0.1
Figure 35-7
with the OSPF neighbor closes (2). BFD notifies the OSPF process that the BFD neighbor is no longer
reachable, and the OSPF process breaks the OSPF neighbor relationship (4). If an alternative path is
available, the routers start converging on it.
Figure 35-7
172.18.0.1
BFD clients are routing protocols that register neighbors with BFD. The switch supports ISIS, OSPF v1
and v2, BGP, EIGRP, and HSRP clients. You can use one BFD session for multiple client protocols. For
example, if a network is running OSPF and EIGRP across the same link to the same peer, you need to
create only one BFD session, and information is shared with both routing protocols.
The switch supports BFD version 0 and version 1. BFD neighbors automatically negotiate the version
and the protocol always runs at the higher version. The default version is version 1.
By default, BFD neighbors exchange both control packets and echo packets for detecting forwarding
failures. The switch sends echo packets at the configured BFD interval rate (from 50 to 999 ms), and
control packets at the BFD slow-timer rate (from 1000 to 3000 ms).
Failure-rate detection can be faster in BFD echo mode, which is enabled by default when you configure
BFD session. In this mode, the switch sends echo packets from the BFD software layer, and the BFD
neighbor responds to the echo packets through its fast-switching layer. The echo packets do not reach
the BFD neighbor software layer, but are reflected back over the forwarding path for failure detection.
You configure the rate at which each BFD interface sends BFD echo packets by entering the bfd interval
interface configuration command.
To reduce bandwidth consumption, you can disable the sending of echo packets by entering the no bfd
echo interface configuration command. When echo mode is disabled, control packets are used to detect
forwarding failures. Control packets are exchanged at the configured slow-timer rate, which could result
in longer failure-detection time. You configure this rate by entering the bfd slow-timer global
configuration command. The range is from 1000 to 3000 ms; the default rate is every 1000 ms.
You can enable or disable echo processing at a switch interface independent of the BFD neighbor
configuration. Disabling echo mode only disables the sending of echo packets by the interface. The
fast-switching layer that receives an echo packet always reflects it back to the sender.
OL-9639-07
Establishing a BFD Session
OSPF
2
BFD
172.16.10.2
Router A
shows what happens when a failure occurs in the network (1). The BFD neighbor session
Breaking an OSPF Neighbor Relationship
OSPF
3
BFD
172.16.10.2
Router A
1
OSPF neighbors
BFD neighbors
3
172.16.10.1
4
OSPF neighbors
X
BFD neighbors
X
2
1
X
172.16.10.1
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Configuring BFD
OSPF
2
BFD
Router B
172.17.0.1
OSPF
3
BFD
Router B
172.17.0.1
35-73