--- /dev/null
+.. _bfd:
+
+**********************************
+Bidirectional Forwarding Detection
+**********************************
+
+:abbr:`BFD (Bidirectional Forwarding Detection)` stands for
+Bidirectional Forwarding Detection and it is described and extended by
+the following RFCs:
+
+* :rfc:`5880`
+* :rfc:`5881`
+* :rfc:`5883`
+
+Currently, there are two implementations of the BFD commands in FRR:
+
+* :abbr:`PTM (Prescriptive Topology Manager)`: an external daemon which
+ implements BFD;
+* ``bfdd``: a BFD implementation that is able to talk with remote peers;
+
+This document will focus on the later implementation: *bfdd*.
+
+
+.. _bfd-starting:
+
+Starting BFD
+============
+
+*bfdd* default configuration file is :file:`bfdd.conf`. *bfdd* searches
+the current directory first then |INSTALL_PREFIX_ETC|/bfdd.conf. All of
+*bfdd*'s command must be configured in :file:`bfdd.conf`.
+
+*bfdd* specific invocation options are described below. Common options
+may also be specified (:ref:`common-invocation-options`).
+
+.. program:: bfdd
+
+.. option:: --bfdctl <unix-socket>
+
+ Set the BFD daemon control socket location. If using a non-default
+ socket location.
+
+ /usr/lib/frr/bfdd --bfdctl /tmp/bfdd.sock
+
+
+ The default UNIX socket location is:
+
+ #define BFDD_CONTROL_SOCKET "|INSTALL_PREFIX_STATE|/bfdd.sock"
+
+
+.. _bfd-commands:
+
+BFDd Commands
+=============
+
+.. index:: bfd
+.. clicmd:: bfd
+
+ Opens the BFD daemon configuration node.
+
+.. index:: peer <A.B.C.D|X:X::X:X> [{multihop|local-address <A.B.C.D|X:X::X:X>|interface IFNAME|vrf NAME}]
+.. clicmd:: 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. This option
+ conflicts with `vrf`.
+
+ `vrf` selects which domain we want to use.
+
+.. index:: 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$ifname|vrf NAME$vrfname}]
+.. clicmd:: 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$ifname|vrf NAME$vrfname}]
+
+ Stops and removes the selected peer.
+
+.. index:: show bfd peers [json]
+.. clicmd:: show bfd peers [json]
+
+ Show all configured BFD peers information and current status.
+
+.. index:: show bfd 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|vrf NAME$vrfname}]> [json]
+.. clicmd:: show bfd peer <WORD$label|<A.B.C.D|X:X::X:X>$peer [{multihop|local-address <A.B.C.D|X:X::X:X>$local|interface IFNAME$ifname|vrf NAME$vrfname}]> [json]
+
+ Show status for a specific BFD peer.
+
+
+.. _bfd-peer-config:
+
+Peer Configurations
+-------------------
+
+.. index:: detect-multiplier (2-255)
+.. clicmd:: 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.
+
+.. index:: receive-interval (10-60000)
+.. clicmd:: receive-interval (10-60000)
+
+ Configures the minimum interval that this system is capable of
+ receiving control packets. The default value is 300 milliseconds.
+
+.. index:: transmit-interval (10-60000)
+.. clicmd:: transmit-interval (10-60000)
+
+ The minimum transmission interval (less jitter) that this system
+ wants to use to send BFD control packets.
+
+.. index:: echo-interval (10-60000)
+.. clicmd:: echo-interval (10-60000)
+
+ Configures the minimal echo receive transmission interval that this
+ system is capable of handling.
+
+.. index:: [no] echo-mode
+.. clicmd:: [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).
+
+.. index:: [no] shutdown
+.. clicmd:: [no] shutdown
+
+ Enables or disables the peer. When the peer is disabled an
+ 'administrative down' message is sent to the remote peer.
+
+.. index:: label WORD
+.. clicmd:: label WORD
+
+ Labels a peer with the provided word. This word can be referenced
+ later on other daemons to refer to a specific peer.
+
+
+.. _bfd-bgp-peer-config:
+
+BGP BFD Configuration
+---------------------
+
+.. index:: neighbor <A.B.C.D|X:X::X:X|WORD> bfd
+.. clicmd:: 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.
+
+.. index:: no neighbor <A.B.C.D|X:X::X:X|WORD> bfd
+.. clicmd:: no neighbor <A.B.C.D|X:X::X:X|WORD> bfd
+
+ Removes any notification registration for this neighbor.
+
+
+.. _bfd-configuration:
+
+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 eth0
+ 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 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
+ !
+
+ ! remove a peer
+ no peer 192.168.0.3 vrf foo
+
+
+.. _bfd-status:
+
+Status
+======
+
+You can inspect the current BFD peer status with the following commands:
+
+::
+
+ frr# 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
+
+ frr# 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
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