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.Dd $Mdocdate: September 14 2017 $
.Dt RTADVD 8
.Os
.Sh NAME
.Nm rtadvd
.Nd router advertisement daemon
.Sh SYNOPSIS
.Nm
.Op Fl ds
.Op Fl c Ar configfile
.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.
By default, if an interface direct route is
added/deleted on an advertising interface and no static prefixes are
specified by the configuration file,
.Nm
adds/deletes the corresponding prefix to/from its advertising list,
respectively.
The
.Fl s
option may be used to disable this behavior.
Moreover, if the status of an advertising interface changes,
.Nm
will start or stop sending router advertisements according
to the latest status.
.Pp
Basically, hosts MUST NOT send Router Advertisement messages at any
time (RFC 4861, Section 6.2.4).
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 Ar configfile
Specify an alternate location,
.Ar configfile ,
for the configuration file.
By default,
.Pa /etc/rtadvd.conf
is used.
.It Fl d
Do not daemonize.
If this option is specified,
.Nm
will run in the foreground and log to
.Em stderr .
.It Fl s
Do not add or delete prefixes dynamically.
Only statically configured prefixes, if any, will be advertised.
.El
.Pp
Upon receipt of signal
.Dv SIGUSR1 ,
.Nm
will dump the current internal state into
.Xr syslog 3 .
.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 4861 6.2.5 .
.Sh FILES
.Bl -tag -width "/etc/rtadvd.conf" -compact
.It Pa /etc/rtadvd.conf
The default configuration file.
.El
.Sh EXIT STATUS
.Ex -std rtadvd
.Sh SEE ALSO
.Xr rtadvd.conf 5 ,
.Xr slaacd 8 ,
.Xr syslogd 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.