# 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 some  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.)

    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
         netdefault(8), boot(8), inetd(8), nonamed(8), rarpd(8).

    BUGS
         Under standard Minix this daemon can't listen to 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)