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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 (22.214.171.124) 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 net-
work. 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
Optionally, rdisc can avoid waiting for routers to announce themselves by sending out a
few ROUTER_SOLICITATION messages to the ALL_ROUTERS (126.96.36.199) 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 consid-
ered 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 negative.
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 preference value. It is
-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 <email@example.com>.
icmp(7), inet(7), ping(8).
Deering, S.E.,ed "ICMP Router Discovery Messages", RFC1256, Network Information Center,
SRI International, Menlo Park, Calif., September 1991.
rdisc requires CAP_NET_RAWIO to listen and send ICMP messages and capability 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-routing/iputils-current.tar.gz.
iputils-020927 27 September 2002 RDISC(8)
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