BFD Sessions

A BFD session defines a relationship between TNSR and a peer so they can exchange BFD information and detect link faults. These sessions are configured by using the bfd session <name> command, which enters config-bfd mode, and defines a BFD session using the given word for a name.

Example:

tnsr# conf
tnsr(config)# bfd session otherrouter
tnsr(config-bfd)# interface GigabitEthernet0/14/0
tnsr(config-bfd)# local address 203.0.113.2
tnsr(config-bfd)# peer address 203.0.113.25
tnsr(config-bfd)# desired-min-tx 100000
tnsr(config-bfd)# required-min-rx 100000
tnsr(config-bfd)# detect-multiplier 3
tnsr(config-bfd)# exit
tnsr(config)# exit
tnsr#

Session Parameters

interface <if-name>:
 The Ethernet interface on which to enable BFD
local address <ip-address>:
 The local address used as a source for BFD packets
peer address <ip-address>:
 The remote BFD peer address. The local and remote peer IP addresses must use the same address family (either IPv4 or IPv6)
desired-min-tx <microseconds>:
 The desired minimum transmit interval, in microseconds
required-min-rx <microseconds>:
 The required minimum transmit interval, in microseconds
detect-multiplier <n-packets>:
 A non-zero value that is, roughly speaking, due to jitter, the number of packets that have to be missed in a row to declare the session to be down. Must be between 1 and 255.

Additional parameters for authentication are covered in BFD Session Authentication.

Changing the BFD Administrative State

Under normal conditions the state of a link monitored by BFD is handled automatically. The link state can also be set manually when necessary.

To disable a link and mark it administratively down:

tnsr# bfd session <name>
tnsr(config-bfd) # disable

To remove the administrative down and return the link to BFD management:

tnsr# bfd session <name>
tnsr(config-bfd) # enable

Viewing BFD Session Status

To see the configuration and status of a BFD session, use the show bfd session command:

tnsr# show bfd session
Session Number: 0
    Local IP Addr: 203.0.113.2
    Peer  IP Addr: 203.0.113.25
    State: down
    Required Min Rx Interval: 100000 usec
    Desired Min Tx Interval: 100000 usec
    Detect Multiplier: 3
    BFD Key Id: 123
    Configuration Key Id: 14
    Authenticated: true