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: