<refentry id="rdisc">

<refmeta>
<refentrytitle>rdisc</refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo>iputils-&snapshot;</refmiscinfo>
</refmeta>

<refnamediv>
<refname>rdisc</refname>
<refpurpose>network router discovery daemon</refpurpose>
</refnamediv>

<refsynopsisdiv>
<cmdsynopsis>
<command>rdisc</command>
<arg choice="opt"><option>-abdfstvV</option></arg>
<arg choice="opt"><replaceable/send_address/</arg>
<arg choice="opt"><replaceable/receive_address/</arg>
</cmdsynopsis>
</refsynopsisdiv>

<refsect1><title>DESCRIPTION</title>
<para>
<command/rdisc/ implements client side of the ICMP router discover protocol.
<command/rdisc/ is invoked at boot time to populate the network
routing tables with default routes. 
</para>

<para>
<command/rdisc/ listens on the ALL_HOSTS (224.0.0.1) multicast address
(or <replaceable/receive_address/ 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.
</para>

<para>
Optionally, <command/rdisc/ 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 <replaceable/send_address/ provided it is given) 
when it is started.
</para>

<para>
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 
<emphasis/advertise/ message is received from the router.
The address will also be excluded from consideration if the host receives an 
<emphasis/advertise/
message with the preference being maximally negative.
</para>

<para>
Server side of router discovery protocol is supported by Cisco IOS
and by any more or less complete UNIX routing daemon, f.e <command/gated/.
</para>

</refsect1>

<refsect1><title>OPTIONS</title>

<variablelist>
 <varlistentry>
  <term><option/-a/</term>
  <listitem><para>
Accept all routers independently of the preference they have in their 
<emphasis/advertise/ messages.
Normally <command/rdisc/ only accepts (and enters in the kernel routing
tables) the router or routers with the highest preference.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-b/</term>
  <listitem><para>
Opposite to <option/-a/, i.e. install only router with the best
preference value. It is default behaviour.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-d/</term>
  <listitem><para>
Send debugging messages to syslog.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-f/</term>
  <listitem><para>
Run <command/rdisc/ forever even if no routers are found.
Normally <command/rdisc/ gives up if it has not received any 
<emphasis/advertise/ message after after soliciting three times,
in which case it exits with a non-zero exit code.
If <option/-f/ is not specified in the first form then 
<option/-s/ must be specified.
  </para></listitem>
 </varlistentry>

 <varlistentry>
  <term><option/-s/</term>
  <listitem><para>
Send three <emphasis/solicitation/ messages initially to quickly discover
the routers when the system is booted.
When <option/-s/ is specified <command/rdisc/
exits with a non-zero exit code if it can not find any routers.
This can be overridden with the <option/-f/ option.
  </para></listitem>
 </varlistentry>

 <varlistentry>
  <term><option/-t/</term>
  <listitem><para>
Test mode. Do not go to background.
  </para></listitem>
 </varlistentry>


 <varlistentry>
  <term><option/-v/</term>
  <listitem><para>
Be verbose i.e. send lots of debugging messages to syslog.
  </para></listitem>
 </varlistentry>

 <varlistentry>
  <term><option/-V/</term>
  <listitem><para>
Print version and exit.
  </para></listitem>
 </varlistentry>
</variablelist>
</refsect1>

<refsect1><title>HISTORY</title>
<para>
This program was developed by Sun Microsystems (see copyright
notice in source file). It was ported to Linux by
<ulink url="mailto:kuznet@ms2.inr.ac.ru">Alexey Kuznetsov
&lt;kuznet@ms2.inr.ac.ru&gt;</ulink>.
It is now maintained by
<ulink url="mailto:yoshfuji@skbuff.net">YOSHIFUJI Hideaki
&lt;yoshfuji@skbuff.net&gt;</ulink>.
</para>
</refsect1>


<refsect1><title>SEE ALSO</title>
<para>
<citerefentry><refentrytitle/icmp/<manvolnum/7/</citerefentry>,
<citerefentry><refentrytitle/inet/<manvolnum/7/</citerefentry>,
<link linkend="ping">
<citerefentry><refentrytitle/ping/<manvolnum/8/</citerefentry></link>.
</para>
</refsect1>

<refsect1><title>REFERENCES</title>
<para>
Deering, S.E.,ed "ICMP Router Discovery Messages",
<ulink url="ftp://ftp.isi.edu/in-notes/rfc1256.txt">
RFC1256</ulink>, Network Information Center, SRI International,
Menlo Park, Calif., September 1991.
</para>
</refsect1>

<refsect1><title>SECURITY</title>
<para>
<command/rdisc/ requires <constant/CAP_NET_RAWIO/ to listen
and send ICMP messages and capability <constant/CAP_NET_ADMIN/
to update routing tables. 
</para>
</refsect1>

<refsect1><title>AVAILABILITY</title>
<para>
<command/rdisc/ is part of <filename/iputils/ package
and the latest versions are  available in source form at
<ulink url="http://www.skbuff.net/iputils/iputils-current.tar.bz2">
http://www.skbuff.net/iputils/iputils-current.tar.bz2</ulink>.
</para>
</refsect1>

<![IGNORE[
<refsect1><title>COPYING</title>
<para>
<literallayout>
Rdisc (this program) was developed by Sun Microsystems, Inc. and is 
provided for unrestricted use provided that this legend is included on 
all tape media and as a part of the software program in whole or part.  
Users may copy or modify Rdisc without charge, and they may freely 
distribute it.

RDISC IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING THE
WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.

Rdisc is provided with no support and without any obligation on the
part of Sun Microsystems, Inc. to assist in its use, correction,
modification or enhancement.

SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY RDISC
OR ANY PART THEREOF.

In no event will Sun Microsystems, Inc. be liable for any lost revenue
or profits or other special, indirect and consequential damages, even if
Sun has been advised of the possibility of such damages.

Sun Microsystems, Inc.
2550 Garcia Avenue
Mountain View, California  94043
</literallayout>
</para>
</refsect1>
]]>


</refentry>