babeld - ad-hoc network routing daemon
babeld option... [ -- ] interface...
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.
- -m multicast-address
- Specify the link-local multicast address to be
used by the protocol. The default is ff02:0:0:0:0:0:1:6.
- -p port
- Specify the
UDP port number to be used by the protocol. The default is 6696.
- -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 4 seconds.
- -z kind [,factor]
- Enable diversity-sensitive
routing. The value kind defines the diversity algorithm used, and can be
one of 0 (no diversity), 1 (per-interface diversity with no memory), 2 (per-channel
diversity with no memory), or 3 (per-channel diversity with memory). The
value factor specifies by how much the cost of non-interfering routes is
multiplied, in units of 1/256; the default is 128 (i.e. division by 2).
- -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.
- -u
- Do not flush unfeasible (useless) routes. This is useful in
order to announce more information to a front-end (see -g).
- -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.
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.
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.
- channel channel
- Sets the channel for this interface. The value channel can be either an
integer, or one of the strings interfering or noninterfering. The default
is to autodetect the channel number for wireless interfaces, and noninterfering
for wired interfaces.
- faraway {true|false}
- This specifies whether the network
is "far away", in the sense that networks behind it don’t interfere with
networks in front of it. By default, networks are not far away.
- 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.
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.
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
- /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.
- 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.
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.
Plenty. This is experimental software, run at your own risk.
routed(8)
, route6d(8)
, zebra(8)
, ahcpd(8)
.
Juliusz Chroboczek.
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