.\"	$NetBSD: rtadvd.8,v 1.29 2020/04/21 12:19:44 wiz Exp $
.\"	$KAME: rtadvd.8,v 1.24 2002/05/31 16:16:08 jinmei Exp $
.\"
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.Dd April 21, 2020
.Dt RTADVD 8
.Os
.Sh NAME
.Nm rtadvd
.Nd router advertisement daemon
.Sh SYNOPSIS
.Nm
.Op Fl CDdfs
.Op Fl c Ar configfile
.Op Fl p Ar pidfile
.Ar interface ...
.Sh DESCRIPTION
.Nm
sends router advertisement packets to the specified interfaces.
.Pp
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.
.Pp
Router advertisements can be configured on a per-interface basis, as
described in
.Xr rtadvd.conf 5 .
.Pp
If there is no configuration file entry for an interface,
or if the configuration file does not exist at all,
.Nm
sets all the parameters to their default values.
In particular,
.Nm
reads all the interface routes from the routing table and advertises
them as on-link prefixes.
.Pp
.Nm
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,
.Nm
adds the corresponding prefix to its advertising list.
.Pp
Similarly, when an interface direct route is deleted,
.Nm
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
.Nm
will completely remove the prefix from the advertising list,
and succeeding advertisements will not contain the prefix information.
.Pp
Moreover, if the status of an advertising interface changes,
.Nm
will start or stop sending router advertisements according
to the latest status.
.Pp
The
.Fl s
option may be used to disable this behavior;
.Nm
will not watch the routing table and the whole functionality described
above will be suppressed.
.Pp
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,
.Nm
can be invoked if router lifetime is explicitly set to zero on every
advertising interface.
.Pp
The command line options are:
.Bl -tag -width indent
.\"
.It Fl C
Don't expire the existing configuration on receipt of SIGHUP.
This option is only intended to aid the testing of clients that consume
Router Advertisement messages.
.It Fl c Ar configfile
Specify an alternate location,
.Ar configfile ,
for the configuration file.
By default,
.Pa /etc/rtadvd.conf
is used.
.It Fl D
Instead of printing errors using
.Xr syslog 3
send them to
.Dv stderr .
Also when
.Xr poll 2
fails, exit instead of retrying.
.It Fl d
Print debugging information.
Repeating this option, adds more verbose debugging.
.It Fl f
Foreground mode (useful when debugging).
Log messages will be dumped to stderr when this option is specified.
.\".It Fl m
.\"Enables mobile IPv6 support.
.\"This changes the content of router advertisement option, as well as
.\"permitted configuration directives.
.It Fl p Ar pidfile
Specify an alternate location,
.Ar pidfile ,
for the PID file.
By default,
.Pa /var/run/rtadvd.pid
is used.
.It Fl s
Do not add or delete prefixes dynamically.
Only statically configured prefixes, if any, will be advertised.
.El
.Pp
Use
.Dv SIGHUP
to reload the configuration file
.Pa /etc/rtadvd.conf .
If an invalid parameter is found in the configuration file upon the reload, the
entry will be ignored and the old configuration will be used.
When parameters in an existing entry are updated and the
.Fl C
flag is not used,
.Nm
will send Router Advertisement messages with the old configuration but zero
router lifetime to the interface first, and then start to send a new message.
.Pp
Upon receipt of signal
.Dv SIGUSR1 ,
.Nm
will dump the current internal state into
.Pa /var/run/rtadvd.dump .
.Pp
Use
.Dv SIGTERM
to kill
.Nm
gracefully.
In this case,
.Nm
will transmit router advertisement with router lifetime 0
to all the interfaces
.Pq in accordance with RFC 2461 6.2.5 .
.Sh FILES
.Bl -tag -width /var/run/rtadvd.dumpXX -compact
.It Pa /etc/rtadvd.conf
The default configuration file.
.It Pa /var/run/rtadvd.pid
Contains the PID of the currently running
.Nm .
.It Pa /var/run/rtadvd.dump
The file in which
.Nm
dumps its internal state.
.El
.Sh EXIT STATUS
.Ex -std rtadvd
.Sh SEE ALSO
.Xr rtadvd.conf 5 ,
.Xr rtsol 8
.Sh HISTORY
The
.Nm
command first appeared in the WIDE Hydrangea IPv6 protocol stack kit.
.Sh BUGS
There used to be some text that recommended users not to let
.Nm
advertise Router Advertisement messages on an upstream link to avoid
undesirable
.Xr icmp6 4
redirect messages.
However, based on 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.