Bidirectional Forwarding Detection

BFD stands for Bidirectional Forwarding Detection and it is described and extended by the following RFCs:

BFDd Commands

bfd: Opens the BFD daemon configuration node.

peer <A.B.C.D|X:X::X:X> [{multihop|local-address <A.B.C.D|X:X::X:X>|interface IFNAME|vrf NAME}]

Creates and configures a new BFD peer to listen and talk to.

multihop tells the BFD daemon that we should expect packets with TTL less than 254 (because it will take more than one hop) and to listen on the multihop port (4784). When using multi-hop mode echo-mode will not work (see RFC 5883 section 3).

local-address provides a local address that we should bind our peer listener to and the address we should use to send the packets. This option is mandatory for IPv6.

interface selects which interface we should use.

vrf selects which domain we want to use.

no peer <A.B.C.D|X:X::X:X>$peer [{multihop|local-address <A.B.C.D|X:X::X:X>$local|interface IFNAME$ifname|vrf NAME$vrf_name}]: Stops and removes the selected peer.

show bfd [vrf NAME] peers [json]: Show all configured BFD peers information and current status.

show bfd [vrf NAME$vrf_name] peer <WORD$label|<A.B.C.D|X:X::X:X>$peer [{multihop|local-address <A.B.C.D|X:X::X:X>$local|interface IFNAME$ifname}]> [json]: Show status for a specific BFD peer.

Peer Configurations

detect-multiplier (2-255)

Configures the detection multiplier to determine packet loss. The remote transmission interval will be multiplied by this value to determine the connection loss detection timer. The default value is 3.

Example: when the local system has detect-multiplier 3 and the remote system has transmission interval 300, the local system will detect failures only after 900 milliseconds without receiving packets.

receive-interval (10-60000): Configures the minimum interval that this system is capable of receiving control packets. The default value is 300 milliseconds.

transmit-interval (10-60000): The minimum transmission interval (less jitter) that this system wants to use to send BFD control packets.

echo-interval (10-60000): Configures the minimal echo receive transmission interval that this system is capable of handling.

[no] echo-mode

Enables or disables the echo transmission mode. This mode is disabled by default.

It is recommended that the transmission interval of control packets to be increased after enabling echo-mode to reduce bandwidth usage. For example: transmission-interval 2000.

Echo mode is not supported on multi-hop setups (see RFC 5883 section 3).

[no] shutdown: Enables or disables the peer. When the peer is disabled an ‘administrative down’ message is sent to the remote peer.

label WORD: Labels a peer with the provided word. This word can be referenced later on other daemons to refer to a specific peer.

BGP BFD Configuration

The following commands are available inside the BGP configuration node.

neighbor <A.B.C.D|X:X::X:X|WORD> bfd: Listen for BFD events registered on the same target as this BGP neighbor. When BFD peer goes down it immediately asks BGP to shutdown the connection with its neighbor and, when it goes back up, notify BGP to try to connect to it.

no neighbor <A.B.C.D|X:X::X:X|WORD> bfd: Removes any notification registration for this neighbor.

neighbor <A.B.C.D|X:X::X:X|WORD> bfd check-control-plane-failure: Allow to write CBIT independence in BFD outgoing packets. Also allow to read both C-BIT value of BFD and lookup BGP peer status. This command is useful when a BFD down event is caught, while the BGP peer requested that local BGP keeps the remote BGP entries as staled if such issue is detected. This is the case when graceful restart is enabled, and it is wished to ignore the BD event while waiting for the remote router to restart.

no neighbor <A.B.C.D|X:X::X:X|WORD> bfd check-control-plane-failure: Disallow to write CBIT independence in BFD outgoing packets. Also disallow to ignore BFD down notification. This is the default behaviour.

OSPF BFD Configuration

The following commands are available inside the interface configuration node.

ip ospf bfd: Listen for BFD events on peers created on the interface. Every time a new neighbor is found a BFD peer is created to monitor the link status for fast convergence.

no ip ospf bfd: Removes any notification registration for this interface peers.

OSPF6 BFD Configuration

The following commands are available inside the interface configuration node.

ipv6 ospf6 bfd: Listen for BFD events on peers created on the interface. Every time a new neighbor is found a BFD peer is created to monitor the link status for fast convergence.

no ipv6 ospf6 bfd: Removes any notification registration for this interface peers.

Configuration

Before applying bfdd rules to integrated daemons (like BGPd), we must create the corresponding peers inside the bfd configuration node.

Here is an example of BFD configuration:

bfd
 peer 192.168.0.1
   label home-peer
   no shutdown
 !
!
router bgp 65530
 neighbor 192.168.0.1 remote-as 65531
 neighbor 192.168.0.1 bfd
 neighbor 192.168.0.2 remote-as 65530
 neighbor 192.168.0.2 bfd
 neighbor 192.168.0.3 remote-as 65532
 neighbor 192.168.0.3 bfd
!

Peers can be identified by its address (use multihop when you need to specify a multi hop peer) or can be specified manually by a label.

Here are the available peer configurations:

bfd

 ! configure a peer on an specific interface
 peer 192.168.0.1 interface ge0
  no shutdown
 !

 ! configure a multihop peer
 peer 192.168.0.2 multihop local-address 192.168.0.3
   shutdown
 !

 ! configure a peer in a different vrf
 peer 192.168.0.3 vrf vrf-foo
  shutdown
 !

 ! configure a peer with every option possible
 peer 192.168.0.4
  label peer-label
  detect-multiplier 50
  receive-interval 60000
  transmit-interval 3000
  shutdown
 !

 ! configure a peer on an interface from a separate vrf
 peer 192.168.0.5 interface ge1 vrf vrf2
  no shutdown
 !

 ! remove a peer
 no peer 192.168.0.3 vrf vrf-foo

Status

You can inspect the current BFD peer status with the following commands:

soodar# show bfd peers
BFD Peers:
        peer 192.168.0.1
                ID: 1
                Remote ID: 1
                Status: up
                Uptime: 1 minute(s), 51 second(s)
                Diagnostics: ok
                Remote diagnostics: ok
                Local timers:
                        Receive interval: 300ms
                        Transmission interval: 300ms
                        Echo transmission interval: disabled
                Remote timers:
                        Receive interval: 300ms
                        Transmission interval: 300ms
                        Echo transmission interval: 50ms

        peer 192.168.1.1
                label: router3-peer
                ID: 2
                Remote ID: 2
                Status: up
                Uptime: 1 minute(s), 53 second(s)
                Diagnostics: ok
                Remote diagnostics: ok
                Local timers:
                        Receive interval: 300ms
                        Transmission interval: 300ms
                        Echo transmission interval: disabled
                Remote timers:
                        Receive interval: 300ms
                        Transmission interval: 300ms
                        Echo transmission interval: 50ms

soodar# show bfd peer 192.168.1.1
BFD Peer:
            peer 192.168.1.1
                label: router3-peer
                ID: 2
                Remote ID: 2
                Status: up
                Uptime: 3 minute(s), 4 second(s)
                Diagnostics: ok
                Remote diagnostics: ok
                Local timers:
                        Receive interval: 300ms
                        Transmission interval: 300ms
                        Echo transmission interval: disabled
                Remote timers:
                        Receive interval: 300ms
                        Transmission interval: 300ms
                        Echo transmission interval: 50ms

soodar# show bfd peer 192.168.0.1 json
{"multihop":false,"peer":"192.168.0.1","id":1,"remote-id":1,"status":"up","uptime":161,"diagnostic":"ok","remote-diagnostic":"ok","receive-interval":300,"transmit-interval":300,"echo-interval":50,"remote-receive-interval":300,"remote-transmit-interval":300,"remote-echo-interval":50}

You can also inspect peer session counters with the following commands:

soodar# show bfd peers counters
BFD Peers:
     peer 192.168.2.1 interface ge2
             Control packet input: 28 packets
             Control packet output: 28 packets
             Echo packet input: 0 packets
             Echo packet output: 0 packets
             Session up events: 1
             Session down events: 0
             Zebra notifications: 2

     peer 192.168.0.1
             Control packet input: 54 packets
             Control packet output: 103 packets
             Echo packet input: 965 packets
             Echo packet output: 966 packets
             Session up events: 1
             Session down events: 0
             Zebra notifications: 4

soodar# show bfd peer 192.168.0.1 counters
     peer 192.168.0.1
             Control packet input: 126 packets
             Control packet output: 247 packets
             Echo packet input: 2409 packets
             Echo packet output: 2410 packets
             Session up events: 1
             Session down events: 0
             Zebra notifications: 4

soodar# show bfd peer 192.168.0.1 counters json
{"multihop":false,"peer":"192.168.0.1","control-packet-input":348,"control-packet-output":685,"echo-packet-input":6815,"echo-packet-output":6816,"session-up":1,"session-down":0,"zebra-notifications":4}