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<refentry id='rdisc8'>
<refmeta>
  <refentrytitle>RDISC</refentrytitle>
  <manvolnum>8</manvolnum>
  <refmiscinfo class='manual'>iputils</refmiscinfo>
</refmeta>
<refnamediv>
  <refname>rdisc</refname>
  <refpurpose>network router discovery daemon</refpurpose>
</refnamediv>
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<refsynopsisdiv id='synopsis'>
  <cmdsynopsis>
    <command>rdisc</command>
    <arg choice='opt'>-abdfrstvV </arg>
    <arg choice='opt'>-p <replaceable>preference</replaceable></arg>
    <arg choice='opt'>-T <replaceable>max_interval</replaceable></arg>
    <arg choice='opt'><replaceable>send_address</replaceable></arg>
    <arg choice='opt'><replaceable>receive_address</replaceable></arg>
    <sbr/>
  </cmdsynopsis>
</refsynopsisdiv>

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

  <para><command>rdisc</command> listens on the ALL_HOSTS (224.0.0.1) multicast address
(or <emphasis remap='I'>receive_address</emphasis> 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</command> 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 <emphasis remap='I'>send_address</emphasis> 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 remap='B'>advertise</emphasis> message is received from the router.
The address will also be excluded from consideration if the host receives an
<emphasis remap='B'>advertise</emphasis>
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 <emphasis remap='B'>gated</emphasis>.
Or, <command>rdisc</command> can act as responder, if compiled with -DRDISC_SERVER.</para>
</refsect1>

<refsect1 id='options'>
  <title>OPTIONS</title>
<variablelist remap='TP'>
  <varlistentry>
  <term><option>-a</option></term>
  <listitem>
<para>Accept all routers independently of the preference they have in their
<emphasis remap='B'>advertise</emphasis> messages.
Normally <command>rdisc</command> only accepts (and enters in the kernel routing
tables) the router or routers with the highest preference.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-b</option></term>
  <listitem>
<para>Opposite to <option>-a</option>, i.e. install only router with the best
preference value. It is default behaviour.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-d</option></term>
  <listitem>
<para>Send debugging messages to syslog.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-f</option></term>
  <listitem>
<para>Run <command>rdisc</command> forever even if no routers are found.
Normally <command>rdisc</command> gives up if it has not received any
<emphasis remap='B'>advertise</emphasis> message after after soliciting three times,
in which case it exits with a non-zero exit code.
If <option>-f</option> is not specified in the first form then
<option>-s</option> must be specified.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-r</option></term>
  <listitem>
<para>Responder mode, available only if compiled with -DRDISC_SERVER.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-s</option></term>
  <listitem>
<para>Send three <emphasis remap='B'>solicitation</emphasis> messages initially to quickly discover
the routers when the system is booted.
When <option>-s</option> is specified <command>rdisc</command>
exits with a non-zero exit code if it can not find any routers.
This can be overridden with the <option>-f</option> option.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-p </option><emphasis remap='I'>preference</emphasis></term>
  <listitem>
<para>Set preference in advertisement.
Available only with -r option.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-T </option><emphasis remap='I'>max_interval</emphasis></term>
  <listitem>
<para>Set maximum advertisement interval in seconds.  Default is 600 secs.
Available only with -r option.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-t</option></term>
  <listitem>
<para>Test mode. Do not go to background.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-v</option></term>
  <listitem>
<para>Be verbose i.e. send lots of debugging messages to syslog.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>-V</option></term>
  <listitem>
<para>Print version and exit.</para>
  </listitem>
  </varlistentry>
</variablelist>
</refsect1>

<refsect1 id='history'>
  <title>HISTORY</title>
  <para>This program was developed by Sun Microsystems (see copyright
notice in source file). It was ported to Linux by
Alexey Kuznetsov&lt;kuznet@ms2.inr.ac.ru&gt;.</para>
</refsect1>

<refsect1 id='see_also'>
  <title>SEE ALSO</title>
  <para><citerefentry><refentrytitle>icmp</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>inet</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>ping</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</refsect1>

<refsect1 id='references'>
  <title>REFERENCES</title>
  <para>Deering, S.E.,ed "ICMP Router Discovery Messages",
RFC1256, Network Information Center, SRI International,
Menlo Park, Calif., September 1991.</para>
</refsect1>

<refsect1 id='security'>
  <title>SECURITY</title>
  <para><command>rdisc</command> requires CAP_NET_RAW to listen
and send ICMP messages and capability CAP_NET_ADMIN
to update routing tables.</para>
</refsect1>

<refsect1 id='availability'>
  <title>AVAILABILITY</title>
  <para><command>rdisc</command> is part of <emphasis remap='I'>iputils</emphasis> package.</para>
</refsect1>
</refentry>