NAME
babeld - ad-hoc network routing daemon
SYNOPSIS
babeld option... [ -- ] interface...
DESCRIPTION
Babel is a loop-avoiding distance-vector routing protocol roughly based
on DSDV and AODV, but with provisions for link cost estimation and
redistribution of routes from other routing protocols.
While it is optimised for wireless mesh networks, Babel will also work
efficiently on wired networks.
OPTIONS
-m multicast-address
Specify the link-local multicast address to be used by the
protocol. The default is ff02::cca6:c0f9:e182:5373.
-p port
Specify the UDP port number to be used by the protocol. The
default is 8475.
-S state-file
Set the name of the file used for preserving long-term
information between invocations of the babeld daemon. If this
file is deleted, the daemon will run in passive mode for 3
minutes when it is next started (see -P below), and other hosts
might initially ignore it. The default is /var/lib/babel-state.
-h hello-interval
Specify the interval in seconds at which scheduled hello packets
are sent on wireless interfaces. The default is 4 seconds.
-H wired-hello-interval
Specify the interval in seconds at which scheduled hello packets
are sent on wired interfaces. The default is 20 seconds.
-i idle-hello-interval
Enable detection of idle networks (networks on which we haven’t
received a hello packet in the last 5 minutes) and specify the
interval in seconds at which scheduled hello packets are sent on
idle interfaces. This functionality is experimental, don’t use
it unless you know what you are doing.
-k priority
Specify the priority value used when installing routes into the
kernel. The default is 0.
-A priority
Allow duplicating external routes when their kernel priority is
at least priority. Do not use this option unless you know what
you are doing, as it can cause persistent route flapping.
-l Use IFF_RUNNING (carrier sense) when determining interface
availability.
-w Don’t optimise wired links, assume all interfaces are wireless
unless explicitly overridden in the configuration file.
-s Do not perform split-horizon processing on wired interfaces.
Split-horizon is not performed on wireless interfaces.
-P Run in parasitic (passive) mode. The daemon will only announce
redistributed routes.
-d level
Debug level. A value of 1 requests a routing table dump at
every iteration through the daemon’s main loop. A value of 2
additionally requests tracing every message sent or received. A
value of 3 additionally dumps all interactions with the OS
kernel. The default is 0.
-g port
Listen for connections from a front-end on port port.
-t table
Use the given kernel routing table for routes inserted by
babeld.
-T table
Export routes from the given kernel routing table.
-c filename
Specify the name of the configuration file. The default is
/etc/babeld.conf.
-C statement
Specify a configuration statement directly on the command line.
-D Daemonise at startup.
-L logfile
Specify a file to log random ‘‘how do you do?’’ messages to.
This defaults to standard error if not daemonising, and to
/var/log/babeld.log otherwise.
-I pidfile
Specify a file to write our process id to. The default is
/var/run/babeld.pid.
interface...
The list of interfaces on which the protocol should operate.
CONFIGURATION FILE FORMAT
The configuration file is a sequence of lines each of which specifies
either an interface or a filtering rule. Blank lines are ignored.
Comments are introduced with an octothorp ‘‘#’’ and terminate at the
end of the line.
Interface configuration
An interface is configured by a single line with the following format:
interface name [parameter...]
Name is the name of the interface (something like eth0).
Each parameter specifies a parameter of the given interface. It can be
one of:
wired {true|false|auto}
This specifies whether to enable optimisations specific to wired
interfaces. By default, this is determined automatically unless
the -w command-line flag was specified.
link-quality {true|false|auto}
This specifies whether link quality estimation should be
performed on this interface. The default is to perform link
quality estimation on wireless interfaces but not on wired
interfaces.
split-horizon {true|false|auto}
This specifies whether to perform split-horizon processing on
this interface. The default is to never perform split-horizon
processing on wireless interfaces; on wired interfaces, the
default depends on the -s flag.
rxcost cost
This defines the cost of receiving frames on the given interface
under ideal conditions (no packet loss); how this relates to the
actual cost used for computing metrics of routes going through
this interface depends on whether link quality estimation is
being done. The default is 96 for wired interfaces, and 256 for
wireless ones.
hello-interval interval
This defines the interval between hello packets sent on this
interface. The default is specified with the -h and -H command-
line flags.
update-interval interval
This defines the interval between full routing table dumps sent
on this interface; since Babel uses triggered updates and
doesn’t count to infinity, this can be set to a fairly large
value, unless significant packet loss is expected. The default
is four times the hello interval.
Filtering rules
A filtering rule is defined by a single line with the following format:
filter selector... action
Filter specifies the filter to which this entry will be added, and can
be one of in, out, or redistribute.
Each selector specifies the conditions under which the given statement
matches. It can be one of
ip prefix
This entry only applies to routes in the given prefix.
eq plen
This entry only applies to routes with a prefix length equal to
plen.
le plen
This entry only applies to routes with a prefix length less or
equal to plen.
ge plen
This entry only applies to routes with a prefix length greater
or equal to plen.
neigh address
This entry only applies to routes learned from a neighbour with
link-local address address.
id id This entry only applies to routes originated by a router with
router-id id.
proto p
This entry only applies to kernel routes with kernel protocol
number p. If neither proto nor local is specified, this entry
applies to all non-local kernel routes with a protocol different
from "boot".
local This entry only applies to local addresses.
if interface
For an input filter, this specifies the interface over which the
route is learned. For an output filter, this specifies the
interface over which this route is advertised. For a
redistribute statement, this specifies the interface over which
the route forwards packets.
Action specifies the action to be taken when this entry matches. It
can have one of the following values:
allow Allow this route, without changing its metric (or setting its
metric to 0 in case of a redistribute filter).
deny Ignore this route.
metric value
For an input or output filter, allow this route after increasing
its metric by value. For a redistribute filter, redistribute
this route with metric value.
If action is not specified, it defaults to allow.
By default, babeld redistributes all local addresses, and no other
routes. In order to make sure that only the routes you specify are
redistributed, you should include the line
redistribute local deny
as the last line in your configuration file.
EXAMPLES
You can participate in a Babel network by simply running
# babeld wlan0
where wlan0 is the name of your wireless interface.
In order to gateway between multiple interfaces, just list them all on
the command line:
# babeld wlan0 eth0 sit1
On an access point, you’ll probably want to redistribute some external
routes into Babel:
# babeld \
-C ’redistribute metric 256’ \
wlan0
or, if you want to constrain the routes that you redistribute,
# babeld \
-C ’redistribute proto 11 ip ::/0 le 64 metric 256’ \
-C ’redistribute proto 11 ip 0.0.0.0/0 le 24 metric 256’ \
wlan0
FILES
/etc/babeld.conf
The default location of the configuration file.
/var/lib/babel-state
The default location of the file storing long-term state.
/var/run/babeld.pid
The default location of the pid file.
/var/log/babeld.log
The default location of the log file.
SIGNALS
SIGUSR1
Dump Babel’s routing tables to standard output or to the log
file.
SIGUSR2
Check interfaces and kernel routes right now, then reopen the
log file.
SECURITY
Babel is a completely insecure protocol: any attacker able to inject IP
packets with a link-local source address can disrupt the protocol’s
operation. This is no different from unsecured neighbour discovery or
ARP.
Since Babel uses link-local IPv6 packets only, there is no need to
update firewalls to allow forwarding of Babel protocol packets. If
local filtering is being done, UDP datagrams to the port used by the
protocol should be allowed. As Babel uses unicast packets in some
cases, it is not enough to just allow packets destined to Babel’s
multicast address.
BUGS
Plenty. This is experimental software, run at your own risk.
SEE ALSO
routed(8), route6d(8), zebra(8), ahcpd(8).
AUTHOR
Juliusz Chroboczek.