'\" t
.TH "RDISC" "8" "" "iputils s20180629" "iputils"
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.SH "NAME"
rdisc \- network router discovery daemon
.SH "SYNOPSIS"
.HP \w'\fBrdisc\fR\ 'u
\fBrdisc\fR [\-abdfrstvV] [\-p\ \fIpreference\fR] [\-T\ \fImax_interval\fR] [\fIsend_address\fR] [\fIreceive_address\fR]
.br

.SH "DESCRIPTION"
.PP
\fBrdisc\fR
implements client side of the ICMP router discover protocol\&.
\fBrdisc\fR
is invoked at boot time to populate the network routing tables with default routes\&.
.PP
\fBrdisc\fR
listens on the ALL_HOSTS (224\&.0\&.0\&.1) multicast address (or
\fIreceive_address\fR
provided it is given) for ROUTER_ADVERTISE messages from routers\&. The received messages are handled by first ignoring those listed router addresses with which the host does not share a network\&. Among the remaining addresses the ones with the highest preference are selected as default routers and a default route is entered in the kernel routing table for each one of them\&.
.PP
Optionally,
\fBrdisc\fR
can avoid waiting for routers to announce themselves by sending out a few ROUTER_SOLICITATION messages to the ALL_ROUTERS (224\&.0\&.0\&.2) multicast address (or
\fIsend_address\fR
provided it is given) when it is started\&.
.PP
A timer is associated with each router address and the address will no longer be considered for inclusion in the the routing tables if the timer expires before a new
\fBadvertise\fR
message is received from the router\&. The address will also be excluded from consideration if the host receives an
\fBadvertise\fR
message with the preference being maximally negative\&.
.PP
Server side of router discovery protocol is supported by Cisco IOS and by any more or less complete UNIX routing daemon, f\&.e
\fBgated\fR\&. Or,
\fBrdisc\fR
can act as responder, if compiled with \-DRDISC_SERVER\&.
.SH "OPTIONS"
.PP
\fB\-a\fR
.RS 4
Accept all routers independently of the preference they have in their
\fBadvertise\fR
messages\&. Normally
\fBrdisc\fR
only accepts (and enters in the kernel routing tables) the router or routers with the highest preference\&.
.RE
.PP
\fB\-b\fR
.RS 4
Opposite to
\fB\-a\fR, i\&.e\&. install only router with the best preference value\&. It is default behaviour\&.
.RE
.PP
\fB\-d\fR
.RS 4
Send debugging messages to syslog\&.
.RE
.PP
\fB\-f\fR
.RS 4
Run
\fBrdisc\fR
forever even if no routers are found\&. Normally
\fBrdisc\fR
gives up if it has not received any
\fBadvertise\fR
message after after soliciting three times, in which case it exits with a non\-zero exit code\&. If
\fB\-f\fR
is not specified in the first form then
\fB\-s\fR
must be specified\&.
.RE
.PP
\fB\-r\fR
.RS 4
Responder mode, available only if compiled with \-DRDISC_SERVER\&.
.RE
.PP
\fB\-s\fR
.RS 4
Send three
\fBsolicitation\fR
messages initially to quickly discover the routers when the system is booted\&. When
\fB\-s\fR
is specified
\fBrdisc\fR
exits with a non\-zero exit code if it can not find any routers\&. This can be overridden with the
\fB\-f\fR
option\&.
.RE
.PP
\fB\-p \fR\fIpreference\fR
.RS 4
Set preference in advertisement\&. Available only with \-r option\&.
.RE
.PP
\fB\-T \fR\fImax_interval\fR
.RS 4
Set maximum advertisement interval in seconds\&. Default is 600 secs\&. Available only with \-r option\&.
.RE
.PP
\fB\-t\fR
.RS 4
Test mode\&. Do not go to background\&.
.RE
.PP
\fB\-v\fR
.RS 4
Be verbose i\&.e\&. send lots of debugging messages to syslog\&.
.RE
.PP
\fB\-V\fR
.RS 4
Print version and exit\&.
.RE
.SH "HISTORY"
.PP
This program was developed by Sun Microsystems (see copyright notice in source file)\&. It was ported to Linux by Alexey Kuznetsov<kuznet@ms2\&.inr\&.ac\&.ru>\&.
.SH "SEE ALSO"
.PP
\fBicmp\fR(7),
\fBinet\fR(7),
\fBping\fR(8)\&.
.SH "REFERENCES"
.PP
Deering, S\&.E\&.,ed "ICMP Router Discovery Messages", RFC1256, Network Information Center, SRI International, Menlo Park, Calif\&., September 1991\&.
.SH "SECURITY"
.PP
\fBrdisc\fR
requires CAP_NET_RAW to listen and send ICMP messages and capability CAP_NET_ADMIN to update routing tables\&.
.SH "AVAILABILITY"
.PP
\fBrdisc\fR
is part of
\fIiputils\fR
package\&.
