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Linux behind a cisco router
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IRDPD(8) System Manager's Manual IRDPD(8) NAME
irdpd - internet router discovery protocol daemon SYNOPSIS
irdpd [-bsd] [-U udp-device] [-I ip-device] [-o priority-offset] DESCRIPTION
Irdpd looks for routers. This should be a simple task, but many routers are hard to find because they do not implement the router discov- ery 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.) OPTIONS
-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 without adverts. -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. -o priority-offset Offset used to make the gateway's preferences collected from RIP packets look worse than those found in genuine router adverts. By default -1024. SEE ALSO
set_net_default(8), boot(8), inetd(8), nonamed(8), rarpd(8). BUGS
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 switch back. 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 blind afterwards. AUTHOR
Kees J. Bot (kjb@cs.vu.nl) IRDPD(8)
