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+.. _babel:
+
+*****
+Babel
+*****
+
+Babel is an interior gateway protocol that is suitable both for wired networks
+and for wireless mesh networks.  Babel has been described as 'RIP on speed' --
+it is based on the same principles as RIP, but includes a number of refinements
+that make it react much faster to topology changes without ever counting to
+infinity, and allow it to perform reliable link quality estimation on wireless
+links.  Babel is a double-stack routing protocol, meaning that a single Babel
+instance is able to perform routing for both IPv4 and IPv6.
+
+FRR implements Babel as described in :rfc:`6126`.
+
+.. _configuring-babeld:
+
+Configuring babeld
+==================
+
+The *babeld* daemon can be invoked with any of the common
+options (:ref:`common-invocation-options`).
+
+The *zebra* daemon must be running before *babeld* is
+invoked. Also, if *zebra* is restarted then *babeld*
+must be too.
+
+Configuration of *babeld* is done in its configuration file
+:file:`babeld.conf`.
+
+.. _babel-configuration:
+
+Babel configuration
+===================
+
+.. clicmd:: router babel
+
+   Enable or disable Babel routing.
+
+.. clicmd:: babel diversity
+
+   Enable or disable routing using radio frequency diversity.  This is
+   highly recommended in networks with many wireless nodes.
+   If you enable this, you will probably want to set `babel
+   diversity-factor` and `babel channel` below.
+
+
+.. clicmd:: babel diversity-factor (1-256)
+
+   Sets the multiplicative factor used for diversity routing, in units of
+   1/256; lower values cause diversity to play a more important role in
+   route selection.  The default it 256, which means that diversity plays
+   no role in route selection; you will probably want to set that to 128
+   or less on nodes with multiple independent radios.
+
+.. clicmd:: network IFNAME
+
+   Enable or disable Babel on the given interface.
+
+
+.. clicmd:: babel <wired|wireless>
+
+   Specifies whether this interface is wireless, which disables a number
+   of optimisations that are only correct on wired interfaces.
+   Specifying `wireless` (the default) is always correct, but may
+   cause slower convergence and extra routing traffic.
+
+.. clicmd:: babel split-horizon
+
+   Specifies whether to perform split-horizon on the interface.  Specifying
+   ``no babel split-horizon`` is always correct, while ``babel
+   split-horizon`` is an optimisation that should only be used on symmetric
+   and transitive (wired) networks.  The default is ``babel split-horizon``
+   on wired interfaces, and ``no babel split-horizon`` on wireless
+   interfaces.  This flag is reset when the wired/wireless status of an
+   interface is changed.
+
+
+.. clicmd:: babel hello-interval (20-655340)
+
+   Specifies the time in milliseconds between two scheduled hellos.  On
+   wired links, Babel notices a link failure within two hello intervals;
+   on wireless links, the link quality value is reestimated at every
+   hello interval.  The default is 4000 ms.
+
+
+.. clicmd:: babel update-interval (20-655340)
+
+   Specifies the time in milliseconds between two scheduled updates.  Since
+   Babel makes extensive use of triggered updates, this can be set to fairly
+   high values on links with little packet loss.  The default is 20000 ms.
+
+
+.. clicmd:: babel channel (1-254)
+.. clicmd:: babel channel interfering
+.. clicmd:: babel channel noninterfering
+
+   Set the channel number that diversity routing uses for this interface (see
+   `babel diversity` above).  Noninterfering interfaces are assumed to only
+   interfere with themselves, interfering interfaces are assumed to interfere
+   with all other channels except noninterfering channels, and interfaces with
+   a channel number interfere with interfering interfaces and interfaces with
+   the same channel number.  The default is ``babel channel interfering`` for
+   wireless interfaces, and ``babel channel noninterfering`` for wired
+   interfaces.  This is reset when the wired/wireless status of an interface is
+   changed.
+
+
+.. clicmd:: babel rxcost (1-65534)
+
+   Specifies the base receive cost for this interface.  For wireless
+   interfaces, it specifies the multiplier used for computing the ETX
+   reception cost (default 256); for wired interfaces, it specifies the
+   cost that will be advertised to neighbours.  This value is reset when
+   the wired/wireless attribute of the interface is changed.
+
+.. note::
+   Do not use this command unless you know what you are doing; in most
+   networks, acting directly on the cost using route maps is a better
+   technique.
+
+
+.. clicmd:: babel rtt-decay (1-256)
+
+   This specifies the decay factor for the exponential moving average of
+   RTT samples, in units of 1/256.  Higher values discard old samples
+   faster.  The default is 42.
+
+
+.. clicmd:: babel rtt-min (1-65535)
+
+   This specifies the minimum RTT, in milliseconds, starting from which we
+   increase the cost to a neighbour. The additional cost is linear in
+   (rtt - rtt-min).  The default is 10 ms.
+
+
+.. clicmd:: babel rtt-max (1-65535)
+
+   This specifies the maximum RTT, in milliseconds, above which we don't
+   increase the cost to a neighbour. The default is 120 ms.
+
+
+.. clicmd:: babel max-rtt-penalty (0-65535)
+
+   This specifies the maximum cost added to a neighbour because of RTT, i.e.
+   when the RTT is higher or equal than rtt-max. The default is 150. Setting it
+   to 0 effectively disables the use of a RTT-based cost.
+
+
+.. clicmd:: babel enable-timestamps
+
+   Enable or disable sending timestamps with each Hello and IHU message in
+   order to compute RTT values.  The default is `no babel enable-timestamps`.
+
+
+.. clicmd:: babel resend-delay (20-655340)
+
+   Specifies the time in milliseconds after which an 'important' request or
+   update will be resent.  The default is 2000 ms.  You probably don't want to
+   tweak this value.
+
+
+.. clicmd:: babel smoothing-half-life (0-65534)
+
+   Specifies the time constant, in seconds, of the smoothing algorithm used for
+   implementing hysteresis.  Larger values reduce route oscillation at the cost
+   of very slightly increasing convergence time.  The value 0 disables
+   hysteresis, and is suitable for wired networks.  The default is 4 s.
+
+.. _babel-redistribution:
+
+Babel redistribution
+====================
+
+
+.. clicmd:: redistribute <ipv4|ipv6> KIND
+
+   Specify which kind of routes should be redistributed into Babel.
+
+.. _show-babel-information:
+
+Show Babel information
+======================
+
+These commands dump various parts of *babeld*'s internal state.
+
+
+.. clicmd:: show babel route
+
+
+.. clicmd:: show babel route A.B.C.D
+
+
+.. clicmd:: show babel route X:X::X:X
+
+
+.. clicmd:: show babel route A.B.C.D/M
+
+
+.. clicmd:: show babel route X:X::X:X/M
+
+
+.. clicmd:: show babel interface
+
+
+.. clicmd:: show babel interface IFNAME
+
+
+.. clicmd:: show babel neighbor
+
+
+.. clicmd:: show babel parameters
+
+Babel debugging commands
+========================
+
+   simple: debug babel KIND
+   simple: no debug babel KIND
+
+.. clicmd:: debug babel KIND
+
+   Enable or disable debugging messages of a given kind. ``KIND`` can
+   be one of:
+
+   - ``common``
+   - ``filter``
+   - ``timeout``
+   - ``interface``
+   - ``route``
+   - ``all``
+
+.. note::
+   If you have compiled with the ``NO_DEBUG`` flag, then these commands aren't
+   available.
+
+
+Babel sample configuration file
+===============================
+
+.. code-block:: frr
+
+   debug babel common
+   !debug babel kernel
+   !debug babel filter
+   !debug babel timeout
+   !debug babel interface
+   !debug babel route
+   !debug babel all
+
+   router babel
+   ! network wlan0
+   ! network eth0
+   ! redistribute ipv4 kernel
+   ! no redistribute ipv6 static
+
+   ! The defaults are fine for a wireless interface
+
+   !interface wlan0
+
+   ! A few optimisation tweaks are optional but recommended on a wired interface
+   ! Disable link quality estimation, enable split horizon processing, and
+   ! increase the hello and update intervals.
+
+   !interface eth0
+   ! babel wired
+   ! babel split-horizon
+   ! babel hello-interval 12000
+   ! babel update-interval 36000
+
+   ! log file /var/log/frr/babeld.log
+   log stdout
+