Provided by: babeld_1.13.1+ds-1_amd64 
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
-V Display babeld's version and quit.
-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, 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.
-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.
-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, -g path
Set up a local configuration server on port port or at path in read-only mode. The protocol is
described in the section Local Configuration Protocol below.
-G port, -G path
Set up a local configuration server on port port or at path in read-write mode. This allows any
local user to change babeld's configuration, and may therefore be a security issue.
-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, use no pidfile if set to the empty string. 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. Comments 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.
reflect-kernel-metric {true|false}
Reflect route metrics as kernel priorities. The priority effectively used is kernel-priority +
metric.
allow-duplicates priority
This allows 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.
random-id {true|false}
This specifies whether to use a random router-id, and is equivalent to the command-line option -r.
ipv6-subtrees {true|false}
This specifies whether to use native source-specific IPv6 forwarding rather than multiple routing
tables. The default is chosen automatically depending on the kernel version.
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 connections from a configuration
client in read-only mode, and is equivalent to the command-line option -g.
local-port-readwrite port
This specifies the TCP port on which babeld will listen for connections from a configuration
client in read-write mode, and is equivalent to the command-line option -G. This allows any local
user to change babeld's configuration, and may therefore be a security issue.
local-path path
This specifies the filesystem path to a socket on which babeld will listen for connections from a
configuration client in read-only mode, and is equivalent to the command-line option -g.
local-path-readwrite path
This specifies the filesystem path to a socket on which babeld will listen for connections from a
configuration client in read-write mode, and is equivalent to the command-line option -G. Any
user with write access to that socket will be able to change babeld's configuration.
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.
kernel-check-interval seconds
This specifies the interval between two kernel routing table dumps. The default is 300s (5
minutes). This may be set to 0 in order to never perform periodic kernel dumps.
shutdown-delay-ms milliseconds
During shutdown we first notify neighbours of our imminent shutdown by sending route retractions,
wait for the specified number of milliseconds and then flush kernel routes. This ensures any
inflight traffic is still properly forwarded. You may want to ensure the delay is appropriate for
the maximum delay path in your network. Setting this to zero is permissible.
link-detect {true|false}
This specifies whether to use carrier sense for determining interface availability, and is
equivalent to the command-line option -l.
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.
daemonise {true|false}
This specifies whether to daemonize at startup, and is equivalent to the command-line option -D.
skip-kernel-setup {true|false}
If this flag is set, no kernel (sysctl) setup is performed on startup, and it is assumed that
enabling forwarding, disabling redirects and disabling the reverse-path filter is performed by
other means. This can be useful when running in environments where system permissions prevent
setting kernel parameters, for instance without root permissions or inside a Linux container.
router-id id
Specify the router-id explicitly, as a modified EUI-64 or a MAC-48 address. If two nodes have the
same router-id, bad things will happen. Don't use this option unless you know what you are doing.
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.
first-rule-priority priority
This specifies smallest (highest) rule priority used with source-specific routes. The default is
100.
key id id type {hmac-sha256|blake2s128} value value
Configure a key for use with the key interface option. The type is one of hmac-sha256 or
blake2s128. The value is a hexadecimal string (up to 64 bytes for hmac-sha256, up to 32 bytes for
blake2s128).
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:
type {auto|wired|wireless|tunnel}
The default is auto 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 only.
split-horizon {true|false|auto}
This specifies whether to perform split-horizon processing on this interface. The default is to
perform split-horizon processing on on wired interfaces, unless the -s flag was set.
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 256 if the
interface is wireless, and 96 otherwise.
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 for tunnel interfaces, and false otherwise.
unicast {true|false}
Send multiple copies of TLVs other than Hellos to all neighbours rather than sending a single
multicast packet. The default is false.
rfc6126-compatible {true|false}
Disable some features that are incompatible with RFC 6126 (the older version of the Babel
protocol), such as source-specific routing and RTT estimation over unicast. The default is false.
rtt-decay decay
This specifies the decay factor for the exponential moving average 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 96 if the interface is of type tunnel, and 0 otherwise.
v4-via-v6 {true|false}
Whether to announce IPv4 routes through this interface even when there is no IPv4 address. The
default depends on the kernel version.
probe-mtu {true|false}
Pad all packets containing a Hello TLV to the MTU and disable fragmentation. This will avoid
establishing adjacencies across links with a mis-configured MTU, at the cost of slightly higher
network usage.
key id Enable HMAC security on this interface, and use the key id.
accept-bad-signatures {true|false}
Accept packets with no signature or an incorrect signature. This only has an effect if a key was
configured on an interface. The default is false.
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 (applied to routes
learned from Babel neighbours), out (applied to routes announced to Babel neighbours), redistribute
(applied to routes redistributed from the kernel), or install (applied to routes installed into the
kernel).
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.
src-ip prefix
This entry only applies to routes with a source prefix in the given prefix.
src-eq plen
This entry only applies to routes with a source prefix length equal to plen.
src-le plen
This entry only applies to routes with a source prefix length less or equal to plen.
src-ge plen
This entry only applies to routes with a source 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.
src-prefix prefix
For a redistribute filter, set the source prefix of this route to prefix.
table table
In an install filter, specify the kernel routing table to use. For source-specific routes, this
only works reliably for IPv6, and only when ipv6-subtrees is true.
pref-src ip
Specify the preferred source address to use with this route. Only useful in an install filter.
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.
LOCAL CONFIGURATION INTERFACE
If babeld is invoked with the flag -g, it accepts TCP connections from local clients on the given port
and address ::1 (the IPv6 localhost address), or on the given UNIX-domain socket path if the argument
starts with ‘/’. When a client connects, babeld replies with BABEL followed with the supported version
of the local configuration protocol (currently 1.0). This is followed with a number of informational
lines (version etc.), terminated by ok. The client can then send requests, one per line. To each
request, babeld replies with one or more lines of data terminated by one of ok, no, or bad.
The following requests are currently defined:
• any configuration file directive, including interface;
• flush interface;
• dump;
• monitor and unmonitor;
• quit.
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
Source-specific routing
If your want to redistribute kernel routes as source-specific to the network, with the 2001:DB8:0:1::/64
prefix:
redistribute src-prefix 2001:DB8:0:1::/64
For more information about source-specific routing, please see
Matthieu Boutier and Juliusz Chroboczek. Source-sensitive routing. In Proc. IFIP Networking
2015. 2015.
available online at
http://arxiv.org/pdf/1403.0445v4.pdf
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.
Usage of the -G flag allows any user logged on the local host to change babeld's configuration.
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.
SEE ALSO
routed(8), route6d(8), zebra(8), ahcpd(8).
AUTHOR
Juliusz Chroboczek.
BABELD(8)