irdpd - internet router discovery protocol daemon
irdpd [-bsd] [-U udp-device] [-I ip-device] [-o priority-offset]
Irdpd looks for routers. This should be a simple task, but many routers
are hard to find because they do not implement the router discovery
protocol. This daemon collects information that routers do send out and
makes it available.
At startup irdpd sends out several router solicitation broadcasts. A
good router should respond to this with a router advertisement.
If a router advertisement arrives then no more solicitations are sent.
The TCP/IP server has filled its routing table with the info from the
advertisement, so it now has at least one router. If the advertisement
is sent by a genuine router (the sender is in the table) then the irdpd
daemon goes dormant for the time the advert is valid. Routers send new
adverts periodically, keeping the daemon silent.
Otherwise irdpd will listen for RIP (Router Information Protocol)
packets. These packets are sent between routers to exchange routing
information. Irdpd uses this information to build a routing table.
Every now and then a router advertisement is sent to the local host to
give it router information build from the RIP packets.
Lastly, if a router solicitation arrives and there is no router around
that sends advertisements, then irdpd sends an advertisement to the
requestor. Note that this is a direct violation of RFC1256, as no host
is supposed to sent those adverts. But alas the world is not always
perfect, and those adverts make booting hosts find routers quickly with
this help from their brothers. (Of course, they will lose the router
soon if they don't have an irdpd daemon themselves.)
-b Broadcast advertisements instead of sending them to the local host
only. This may be used to keep (non-Minix) hosts alive on a net
-s Be silent, do not send advertisements to hosts that ask for them.
-d Debug mode, tell where info is coming from and where it is sent.
Debugging can also be turned on at runtime by sending signal SIGUSR1
or turned off with SIGUSR2.
Offset used to make the gateway's preferences collected from RIP
packets look worse than those found in genuine router adverts. By
set_net_default(8), boot(8), inetd(8), nonamed(8), rarpd(8).
Under standard Minix this daemon can't listen to two both IRDP and RIP at
the same time, so it starts out with IRDP. It switches over to RIP if it
can't find a router, or if it threatens to lose its router. It does not
Irdpd may help a host that should not be helped, i.e. if it doesn't have
an irdpd daemon with RIP collecting trickery. It will make System
Administrators pull out their remaining hair trying to find out why a
host can access outside networks for a some time after boot, but goes
Kees J. Bot (email@example.com)