@c -*-texinfo-*-
@c This is part of the FRR Manual.
@c @value{COPYRIGHT_STR}
@c See file frr.texi for copying conditions.
@node Babel
@chapter 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 RFC6126.

@menu
* Configuring babeld::          
* Babel configuration::         
* Babel redistribution::        
* Show Babel information::      
* Babel debugging commands::    
@end menu

@node Configuring babeld, Babel configuration, Babel, Babel
@section Configuring babeld

The @command{babeld} daemon can be invoked with any of the common
options (@pxref{Common Invocation Options}).

The @command{zebra} daemon must be running before @command{babeld} is
invoked. Also, if @command{zebra} is restarted then @command{babeld}
must be too.

Configuration of @command{babeld} is done in its configuration file
@file{babeld.conf}.

@node Babel configuration, Babel redistribution, Configuring babeld, Babel
@section Babel configuration

@deffn Command {router babel} {}
@deffnx Command {no router babel} {}
Enable or disable Babel routing.
@end deffn

@deffn Command {babel resend-delay <20-655340>} {}
Specifies the time after which important messages are resent when
avoiding a black-hole.  The default is 2000@dmn{ms}.
@end deffn

@deffn Command {babel diversity} {}
@deffnx Command {no 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 @code{babel
diversity-factor} and @code{babel channel} below.
@end deffn

@deffn Command {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.
@end deffn

@deffn {Babel Command} {network @var{ifname}} {}
@deffnx {Babel Command} {no network @var{ifname}} {}
Enable or disable Babel on the given interface.
@end deffn

@deffn {Interface Command} {babel wired} {}
@deffnx {Interface Command} {babel wireless} {}
Specifies whether this interface is wireless, which disables a number
of optimisations that are only correct on wired interfaces.
Specifying @code{wireless} (the default) is always correct, but may
cause slower convergence and extra routing traffic.
@end deffn

@deffn {Interface Command} {babel split-horizon}
@deffnx {Interface Command} {no babel split-horizon}
Specifies whether to perform split-horizon on the interface.
Specifying @code{no babel split-horizon} is always correct, while
@code{babel split-horizon} is an optimisation that should only be used
on symmetric and transitive (wired) networks.  The default is
@code{babel split-horizon} on wired interfaces, and @code{no babel
split-horizon} on wireless interfaces.  This flag is reset when the
wired/wireless status of an interface is changed.
@end deffn

@deffn {Interface Command} {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@dmn{ms}.
@end deffn

@deffn {Interface Command} {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@dmn{ms}.
@end deffn

@deffn {Interface Command} {babel channel <1-254>}
@deffnx {Interface Command} {babel channel interfering}
@deffnx {Interface Command} {babel channel noninterfering}
Set the channel number that diversity routing uses for this interface
(see @code{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 @samp{babel channel interfering} for wireless
interfaces, and @samp{babel channel noninterfering} for wired
interfaces.  This is reset when the wired/wireless status of an
interface is changed.
@end deffn

@deffn {Interface Command} {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.

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.
@end deffn

@deffn {Interface Command} {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.
@end deffn

@deffn {Interface Command} {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@dmn{ms}.
@end deffn

@deffn {Interface Command} {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@dmn{ms}.
@end deffn

@deffn {Interface Command} {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 0,
which effectively disables the use of a RTT-based cost.
@end deffn

@deffn {Interface Command} {babel enable-timestamps}
@deffnx {Interface Command} {no babel enable-timestamps}
Enable or disable sending timestamps with each Hello and IHU message in
order to compute RTT values.  The default is @code{no babel
enable-timestamps}.
@end deffn

@deffn {Babel Command} {babel resend-delay <20-655340>}
Specifies the time in milliseconds after which an ``important''
request or update will be resent.  The default is 2000@dmn{ms}.  You
probably don't want to tweak this value.
@end deffn

@deffn {Babel Command} {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@dmn{s}.
@end deffn

@node Babel redistribution, Show Babel information, Babel configuration, Babel
@section Babel redistribution

@deffn {Babel command} {redistribute @var{<ipv4|ipv6>} @var{kind}}
@deffnx {Babel command} {no redistribute @var{<ipv4|ipv6>} @var{kind}}
Specify which kind of routes should be redistributed into Babel.
@end deffn

@node Show Babel information, Babel debugging commands, Babel redistribution, Babel
@section Show Babel information

@deffn {Command} {show babel route} {}
@deffnx {Command} {show babel route A.B.C.D}
@deffnx {Command} {show babel route X:X::X:X}
@deffnx {Command} {show babel route A.B.C.D/M}
@deffnx {Command} {show babel route X:X::X:X/M}
@deffnx {Command} {show babel interface} {}
@deffnx {Command} {show babel interface @var{ifname}} {}
@deffnx {Command} {show babel neighbor} {}
@deffnx {Command} {show babel parameters} {}
These commands dump various parts of @command{babeld}'s internal state.
@end deffn

@node Babel debugging commands,  , Show Babel information, Babel
@section Babel debugging commands

@deffn {Babel Command} {debug babel @var{kind}} {}
@deffnx {Babel Command} {no debug babel @var{kind}} {}
Enable or disable debugging messages of a given kind.  @var{kind} can
be one of @samp{common}, @samp{kernel}, @samp{filter}, @samp{timeout},
@samp{interface}, @samp{route} or @samp{all}.  Note that if you have
compiled with the NO_DEBUG flag, then these commands aren't available.
@end deffn

