BABELD(8)BABELD(8)NAMEbabeld - ad-hoc network routing daemon
SYNOPSISbabeld 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 pro‐
tocol. 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 informa‐
tion 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 ini‐
tially 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 diver‐
sity with no memory), or 3 (per-channel diversity with memory).
The value factor specifies by how much the cost of non-interfer‐
ing routes is multiplied, in units of 1/256; the default is 128
(i.e. division by 2).
-M half-time
Specify the half-time in seconds of the exponential decay used
for smoothing metrics for performing route selection; the value
0 disables smoothing. The default is 4s.
-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.
-r Use a random router-id. The default is to use persistent
router-ids derived from the MAC address of the first interface,
which is easier to debug and more reliably prevents routing
loops but may sometimes cause a node to be unreachable for 120
seconds just after boot.
-u Do not flush unfeasible (useless) routes. This is useful in
order to announce more information to a front-end (see -g).
-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 ker‐
nel. 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. This can be
specified multiple times in order to export routes from more
than one table.
-c filename
Specify the name of the configuration file. This flag can be
repeated multiple times. 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 a
global option, an interface specification or a filtering rule. Com‐
ments are introduced by an octothorp ``#'' and terminate at the end of
the line.
Global options
protocol-group group
This specifies the link-local multicast address to be used by
the protocol, and is equivalent to the command-line option -m.
protocol-port port
This specifies the UDP port number to be used by the protocol,
and is equivalent to the command-line option -p.
kernel-priority priority
This specifies the priority value used when installing routes
into the kernel, and is equivalent to the command-line option
-k.
allow-duplicates priority
This allows duplicating external routes when their kernel prior‐
ity is at least priority. Do not use this option unless you
know what you are doing, as it can cause persistent route flap‐
ping.
keep-unfeasible {true|false}
This specifies whether to keep unfeasible (useless) routes, and
is equivalent to the command-line option -u.
random-id {true|false}
This specifies whether to use a random router-id, and is equiva‐
lent to the command-line option -r.
debug level
This specifies the debugging level, and is equivalent to the
command-line option -d.
local-port port
This specifies the TCP port on which babeld will listen for con‐
nections from a front-end, and is equivalent to the command-line
option -g.
export-table table
This specifies the kernel routing table to use for routes
inserted by babeld, and is equivalent to the command-line option
-t.
import-table table
This specifies a kernel routing table from which routes are
redistributed by babeld, and can be specified multiple times
with a cumulative effect. This is equivalent to the command-
line option -T.
link-detect {true|false}
This specifies whether to use carrier sense for determining
interface availability, and is equivalent to the command-line
option -l.
diversity {true|false|kind}
This specifies the diversity algorithm to use; true is equiva‐
lent to kind 3. The default is false (do not use any diversity
algorithm).
diversity-factor factor
This specifies by how much the cost of non-interfering routes
should be multiplied, in units of 1/256. The default is 128
(division by 2).
smoothing-half-life seconds
This specifies the half-life in seconds of the exponential decay
used for smoothing metrics for performing route selection, and
is equivalent to the command-line option -M.
deamonise {true|false}
This specifies whether to daemonize at startup, and is equiva‐
lent to the command-line option -D.
state-file filename
This specifies the name of the file used for preserving long-
term information between invocations of the babeld daemon, and
is equivalent to the command-line option -S.
log-file filename
This specifies the name of the file used to log random messages
to, and is equivalent to the command-line option -L.
pid-file filename
This specifies the name of the file to which babeld writes out
its process id, and is equivalent to the command-line option -I.
Interface configuration
An interface is configured by a line with the following format:
interface name [parameter...]
where name is the name of the interface (something like eth0). The
default value of an interface parameter can be specified changed by a
line of the form
default [parameter...]
Each parameter 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 per‐
formed on this interface. The default is to perform link qual‐
ity estimation on wireless interfaces but not on wired inter‐
faces.
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 nonin‐
terfering. 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.
enable-timestamps {true|false}
Enable sending timestamps with each Hello and IHU message in
order to compute RTT values. The default is true if
max-rtt-penalty is non-zero (see below), and false otherwise.
rtt-decay decay
This specifies the decay factor for the exponential moving aver‐
age of RTT samples, in units of 1/256. Must be between 1 and
256, inclusive. Higher values discard old samples faster. The
default is 42.
rtt-min rtt
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.
rtt-max rtt
This specifies the maximum RTT, in milliseconds, above which we
don't increase the cost to a neighbour. The default is 120 ms.
max-rtt-penalty cost
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.
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 redis‐
tribute 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 mul‐
ticast address.
BUGS
Plenty. This is experimental software, run at your own risk.
SEE ALSOrouted(8), route6d(8), zebra(8), ahcpd(8).
AUTHOR
Juliusz Chroboczek.
BABELD(8)