rdisc - Unix, Linux Command
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 (188.8.131.52) 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 kernel 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 (184.108.40.206) 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
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.
Accept all routers independently of the preference they have in their
Normally rdisc only accepts (and enters in the kernel routing
tables) the router or routers with the highest preference.
Opposite to -a, i.e. install only router with the best
preference value. It is default behaviour.
Send debugging messages to syslog.
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.
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.
Test mode. Do not go to background.
Be verbose i.e. send lots of debugging messages to syslog.
Print version and exit.
This program was developed by Sun Microsystems (see copyright
notice in source file). It was ported to Linux by
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