Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!rutgers!aramis.rutgers.edu!geneva.rutgers.edu!hedrick From: hedrick@geneva.rutgers.edu (Charles Hedrick) Newsgroups: comp.protocols.tcp-ip Subject: Re: Subnets on an unsubnetted network Message-ID: Date: 31 Jan 89 21:15:10 GMT References: <8901302314.AA07244@Jester.CC.MsState.Edu> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 57 OK, you've got a central network with 130.18.1 to 130.18.63, and a Sun connecting this network to a small Ethernet with 130.18.64 on it. What I think you want to do (and I confess I haven't tried this) is: on the interface to your small Ethernet, leave things as a normal subnet, i.e. subnet mask 255.255.255.0, and broadcast address 130.18.64.255. on the interface on the central network, set the broadcast address (it's a parameter to ifconfig) to 130.18.255.255. I think you want to leave the subnet mask as 255.255.255.0. If you try to use a subnet mask of 255.255.0.0 on this interface, routing is likely to get very confused. route add 0 0 run the proxy ARP daemon. (I'm sure I heard somebody say there was a version that worked under 4.0. It's got to be completely different than the 3.2 version.) The "route add" will cause your Sun to treat any address it doesn't know about as being attached directly to your main network. This assumes that any gateways you have to connect you offsite will respond to ARP requests for addresses offcampus. If your exterior gateway doesn't have a complete proxy ARP implementation (I've heard rumors that this is true for Proteon), then you're going to have to do route add 130.18.1.0 0 route add 130.18.2.0 0 ... for all subnets on the main network. Or if you have one gateway somewhere that knows all your subnets, run routed and get routes from it. I don't see any way to make things work unless you can get proxy ARP running. However if you have a Sun (or other system with similar facilities) anywhere else on the network, you can do arp -s pub for every host on your subnet. This causes the machine to do a kind of hard-wired proxy ARP. When it sees an ARP request for it will respond with . should be the address of the Sun that's acting as the gateway to your subnet. You can't do this on that Sun itself, because it needs to know the actual Ethernet addresses of those machines. By the way, I'm not sure that this whole business is really the right way to do things. The moment you have different machines on your main network with different subnet masks, things will get very exciting. The ICMP subnet mask broadcasts will tend to cause machines to randomly change subnet masks. I think I'd set up every machine that knows about subnet masks to use a mask of 255.255.255.0. Then use the "route add 0" commands as described above to tell it to use the main network for all the subnets.