RTADVD(8) System Manager's Manual RTADVD(8)

rtadvd — router advertisement daemon

rtadvd [-dDfMRs] [-c configfile] [-F dumpfile] [-p pidfile] interface ...

rtadvd sends router advertisement packets to the specified interfaces.

The program will daemonize itself on invocation. It will then send router advertisement packets periodically, as well as in response to router solicitation messages sent by end hosts.

Router advertisements can be configured on a per-interface basis, as described in rtadvd.conf(5).

If there is no configuration file entry for an interface, or if the configuration file does not exist altogether, rtadvd sets all the parameters to their default values. In particular, rtadvd reads all the interface routes from the routing table and advertises them as on-link prefixes.

rtadvd also watches the routing table. If an interface direct route is added on an advertising interface and no static prefixes are specified by the configuration file, rtadvd adds the corresponding prefix to its advertising list.

Similarly, when an interface direct route is deleted, rtadvd will start advertising the prefixes with zero valid and preferred lifetimes to help the receiving hosts switch to a new prefix when renumbering. Note, however, that the zero valid lifetime cannot invalidate the autoconfigured addresses at a receiving host immediately. According to the specification, the host will retain the address for a certain period, which will typically be two hours. The zero lifetimes rather intend to make the address deprecated, indicating that a new non-deprecated address should be used as the source address of a new connection. This behavior will last for two hours. Then rtadvd will completely remove the prefix from the advertising list, and succeeding advertisements will not contain the prefix information.

Moreover, if the status of an advertising interface changes, rtadvd will start or stop sending router advertisements according to the latest status.

The -s option may be used to disable this behavior; rtadvd will not watch the routing table and the whole functionality described above will be suppressed.

Basically, hosts MUST NOT send Router Advertisement messages at any time (RFC 2461, Section 6.2.3). However, it would sometimes be useful to allow hosts to advertise some parameters such as prefix information and link MTU. Thus, rtadvd can be invoked if router lifetime is explicitly set zero on every advertising interface.

The command line options are:

Specify an alternate location, configfile, for the configuration file. By default, /etc/rtadvd.conf is used.
Print debugging information.
Even more debugging information is printed.
This option is now deprecated and ignored.
Specify an alternative file in which to dump internal states when rtadvd receives signal SIGUSR1. The default is /var/run/rtadvd.dump.
Specify an interface to join the all-routers site-local multicast group. By default, rtadvd tries to join the first advertising interface appearing on the command line. This option has meaning only with the -R option, which enables routing renumbering protocol support.
Specify an alternative file in which to store the process ID. The default is /var/run/rtadvd.pid.
Accept router renumbering requests. If you enable it, certain IPsec setup is suggested for security reasons. This option is currently disabled, and is ignored by rtadvd with a warning message.
Do not add or delete prefixes dynamically. Only statically configured prefixes, if any, will be advertised.

Upon receipt of signal SIGUSR1, rtadvd will dump the current internal state into /var/run/rtadvd.dump or the file specified with option -F.

Use SIGTERM to kill rtadvd gracefully. In this case, rtadvd will transmit router advertisement with router lifetime 0 to all the interfaces (in accordance with RFC2461 6.2.5).

/etc/rtadvd.conf
The default configuration file.
/var/run/rtadvd.pid
The default process ID file.
/var/run/rtadvd.dump
The default file in which rtadvd dumps its internal state.

The rtadvd utility exits 0 on success, and >0 if an error occurs.

rtadvd.conf(5)

The rtadvd command first appeared in the WIDE Hydrangea IPv6 protocol stack kit.

There used to be some text that recommended users not to let rtadvd advertise Router Advertisement messages on an upstream link to avoid undesirable icmp6(4) redirect messages. However, based on the later discussion in the IETF ipng working group, all routers should rather advertise the messages regardless of the network topology, in order to ensure reachability.

August 27, 2011 macOS 15.6