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babeld

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.