RDISC(8) System Manager’s Manual: iputils RDISC(8)
rdisc - network router discovery daemon
rdisc [ -abdfstvV] [ send_address] [ receive_address]
rdisc implements client side of the ICMP router discover protocol.
rdisc is invoked at boot time to populate the network routing tables
with default routes.
rdisc listens on the ALL_HOSTS (184.108.40.206) multicast address (or
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 ker-
nel routing table for each one of them.
Optionally, rdisc can avoid waiting for routers to announce themselves
by sending out a few ROUTER_SOLICITATION messages to the ALL_ROUTERS
(220.127.116.11) multicast address (or send_address provided it is given)
when it is started.
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 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
Server side of router discovery protocol is supported by Cisco IOS and
by any more or less complete UNIX routing daemon, f.e gated.
-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.
-b Opposite to -a, i.e. install only router with the best prefer-
ence value. It is default behaviour.
-d Send debugging messages to syslog.
-f Run rdisc forever even if no routers are found. Normally rdisc
gives up if it has not received any advertise message after
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.
-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 Test mode. Do not go to background.
-v Be verbose i.e. send lots of debugging messages to syslog.
-V Print version and exit.
This program was developed by Sun Microsystems (see copyright notice in
source file). It was ported to Linux by Alexey Kuznetsov
icmp(7), inet(7), ping(8).
Deering, S.E.,ed "ICMP Router Discovery Messages", RFC1256, Network
Information Center, SRI International, Menlo Park, Calif., September
rdisc requires CAP_NET_RAWIO to listen and send ICMP messages and capa-
bility CAP_NET_ADMIN to update routing tables.
rdisc is part of iputils package and the latest versions are available
in source form for anonymous ftp ftp://ftp.inr.ac.ru/ip-rout-
iputils-020927 07 April 2005 RDISC(8)
Man(1) output converted with