fitz@wang.com (Tom Fitzgerald) (02/24/90)
Is it possible to have a single Ethernet with multiple IP network addresses on it, and get the separate IP nets talking to each other? Especially, is it possible to do this cheaply? We've got a number of separate Ethernets, with separate IP addresses, that we want to connect together. In the long run, as traffic rises (and equipment becomes available) we'll be putting in proper gateways where they look necessary. But we want to get the machines on the various nets talking to each other ASAP. We don't want to renumber all the IP addresses, since we'd just have to change them back when we started isolating the various nets with gateways. And it may be some time before we can get all the gateways in place. The ideal solution from our point of view would be a "gateway" with a single interface and many IP addresses for it. It would accept all inter-net packets from all logical nets, and send them back out again, as-is, on the same wire, to the right final destination. Are there any gateways or routers that are capable of this? All the ones I have specs on assume that interfaces map one-to-one with logical nets. If there aren't any machines like this, what's the least we could do to get this working? Any and all info appreciated. --- Tom Fitzgerald fitz@wang.com Wang Labs ...!uunet!wang!fitz Lowell MA, USA 1-508-967-5278
kwe@buit13.bu.edu (Kent England) (02/27/90)
In article <1990Feb23.214634.8645@wang.com> fitz@wang.com (Tom Fitzgerald) writes: >Is it possible to have a single Ethernet with multiple IP network addresses >on it, and get the separate IP nets talking to each other? Especially, is >it possible to do this cheaply? > You need to be able to tell your hosts to ARP for all addresses. In other words, you need to make them think that every other host is reachable directly. The net part is zero length; the entire address is "local part". This gets you what you want without the extra hop of a single-interface gateway. If you add a real gateway somewhere at some future time, and if it supports proxy ARP correctly, this will work thru a transition from bridged/repeatered LANs to properly internetted LANs, until such time as you can come back to all your hosts and set a new subnet/net mask and stop using proxy ARP if you choose. However, since there is a "built-in" net mask defining net/local for class A, B, C, etc, this "zero-length" network mask may not work in specific products, depending on how subnet masks were implemented. In fact, it might not be RFC legal. (Must check that Host Requirements RFC again.) I don't know of anyone offhand who is using proxy ARP this aggressively. Most people just use it to handle backward compatibility for the subnet problem between 4.2 and 4.3 BSD. So their hosts are still using the "built-in" class-based mask or are using subnet masks as an "extension", rather than "replacement" of the built-in mask. (Maybe you can set the subnet mask to be a negative number? :-) But this does solve the dynamic gateway discovery problem rather neatly. That's it! Let's do away with net/local altogether and have hosts ask for pathways to every IP address they want. Does that sound like an advanced end-system protocol? :-) Kent England, Boston University
bob@MorningStar.Com (Bob Sutterfield) (02/27/90)
You might try cobbling something up with Proxy ARP to fill in the ARP tables when IP would rather route than ARP.