BABELD(8)

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.