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.
- -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.
- -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).
- -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 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.
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.
- 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.
- 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 equivalent
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.
- 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.
This can be useful when running in environments where system permissions
prevent setting kernel parameters, for instance 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-table-number table
- This specifies the index of the first routing table to use for
source-specific routes. The default is 10.
- first-rule-priority priority
- This specifies smallest (highest) rule priority used with source-specific
routes. The default is 100.
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.
- 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 other 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 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.
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.
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.
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
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
- /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.
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.
routed(8),
route6d(8),
zebra(8),
ahcpd(8).
Juliusz Chroboczek.