RDISC(1M)                                                            RDISC(1M)



NAME
     rdisc - Internet router discovery daemon

SYNOPSIS
     /usr/etc/rdisc [ -sfa ]

     /usr/etc/rdisc -r [ -p preference ] [ -T interval ]

DESCRIPTION
     rdisc implements the ICMP router discover protocol.  The first form of
     the command is used on hosts and the second form is used on routers.  On
     a host rdisc is invoked at boot time to populate the network routing
     tables with default routes. On a router it is also invoked at boot time
     in order to start advertising the router to all the hosts.

   Host (First Form)
     On a host rdisc listens on the ALLHOSTS (224.0.0.1) multicast address
     for ROUTERADVERTISE 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.

     Optionally, rdisc can avoid waiting for routers to announce themselves by
     sending out a few ROUTERSOLICITATION messages to the ALLROUTERS
     (224.0.0.2) multicast address when it is started.

     A timer is associated with each router address and the address will no
     longer be considered for inclusion in the routing tables if the timer
     expires before a new advertise message is received from the router.  The
     address will also be excluded from consideration if the host receives an
     advertise message with the preference being maximally negative.

   Router (Second Form)
     When rdisc is started on a router, it uses the SIOCGIFCONF ioctl(2) to
     find the interfaces configured into the system and it starts listening on
     the ALLROUTERS multicast address on all the interfaces that support
     multicast.  It sends out advertise messages to the ALLHOSTS multicast
     address advertising all its addresses.  A few initial advertise messages
     are sent out during the first 30 seconds and after that it will transmit
     advertise messages approximately every 600 seconds.

     When rdisc receives a solicitation message it sends an advertise message
     to the host that sent the solicitation message.

     When rdisc is terminated by a signal it sends out an advertise message
     with the preference being maximally negative.








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RDISC(1M)                                                            RDISC(1M)



OPTIONS
     -a             Accept all routers independently of the preference they
                    have in their advertise messages.  Normally rdisc only
                    accepts (and enters in the kernel routing tables) the
                    router or routers with the highest preference.

     -f             Run rdisc forever even if no routers are found.  Normally
                    rdisc gives up if it has not received any advertise
                    message after soliciting three times, in which case it
                    exits with a non-zero exit code.  If -f is not specified
                    in the first form then -s must be specified.

     -p preference  Set the preference transmitted in the solicitation
                    messages.  The default is zero.

     -r             Act as a router as opposed to a host.

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

     -T interval    Set the interval between transmitting the advertise
                    messages.  The default time is 600 seconds.

SEE ALSO
     routed(1M) ioctl(2), icmp(7), inet(7)

     Deering, S.E.,ed ``ICMP Router Discovery Messages,'' RFC 1256, Network
     Information Center, SRI International, Menlo Park, Calif., September
     1991.























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