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Cisco ME 3800X and 3600X Switch Software Configuration Guide
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Chapter 29 Configuring IP Unicast Routing
Configuring BFD
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.
To run BFD on a switch, you need to configure basic BFD interval parameters on BFD interfaces, enable
routing on the switch, and enable one or more one routing protocol clients for BFD. You also need to
confirm that Cisco Express Forwarding (CEF) is enabled (the default) on participating switches.
For more detailed configuration, see the Bidirectional Forwarding Detection feature module at this URL:
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/fs_bfd.html
For details on the commands, use the Master Index to the Cisco IOS Command List for Release 12.4. at
this URL:
http://www.cisco.com/en/US/docs/ios/mcl/allreleasemcl/all_book.html
These sections describe configuring BFD:
•
Default BFD Configuration, page 29-72
•
Default BFD Configuration Guidelines, page 29-73
•
Configuring BFD Session Parameters on an Interface, page 29-73
•
Enabling BFD Routing Protocol Clients, page 29-74
Default BFD Configuration
No BFD sessions are configured. BFD is disabled on all interfaces.
When configured, BFD version 1 is the default, but switches negotiate for version. Version 0 is also
supported.
Standby BFD (for HSRP) is enabled by default.
Asynchronous BFD echo mode is enabled when a BFD session is configured.