in.rdisc - network router discovery daemon
SYNOPSIS
in.rdisc [ -sfa ]
in.rdisc -r [ -p preference ] [ -T interval ]
DESCRIPTION
iinn..rrddiisscc 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 iinn..rrddiisscc 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 iinn..rrddiisscc listens on the AALLLL_HHOOSSTTSS (224.0.0.1)
multicast address for RROOUUTTEERR_AADDVVEERRTTIISSEE messages from
routers. The received messages are handled by first ignor
ing 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 rout
ing table for each one of them.
Optionally, iinn..rrddiisscc can avoid waiting for routers to
announce themselves by sending out a few RROOUUTTEERR_SSOOLLIICCIITTAA
TTIIOONN messages to the AALLLL_RROOUUTTEERRSS (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
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 iinn..rrddiisscc is started on a router, it uses the SSIIOOCCGGIIFF
CCOONNFF ioctl(2) to find the interfaces configured into the
system and it starts listening on the AALLLL_RROOUUTTEERRSS multi
cast address on all the interfaces that support multicast.
It sends out advertise messages to the AALLLL_HHOOSSTTSS multicast
address advertising all its addresses. A few initial
advertise messages are sent out during the first 30 sec
onds and after that it will transmit advertise messages
approximately every 600 seconds.
When iinn..rrddiisscc receives a solicitation message it sends an
advertise message to the host that sent the solicitation
message.
advertise message with the preference being maximally neg
ative.
OPTIONS
-a Accept all routers independently of the
preference they have in their advertise
messages. Normally in.rdisc only accepts
(and enters in the kernel routing tables)
the router or routers with the highest
preference.
-f Run in.rdisc forever even if no routers are
found. Normally in.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.
-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
in.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
in.routed(8C) 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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