Path: utzoo!utgpu!water!watmath!clyde!att!ucbvax!proteon.COM!jas From: jas@proteon.COM (John A. Shriver) Newsgroups: comp.protocols.tcp-ip Subject: subnet IP mask stored in route or interface struct? Message-ID: <8808041418.AA01360@monk.proteon.com> Date: 4 Aug 88 14:18:57 GMT References: <962@rlgvax.UUCP> Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 29 Your configuration is illegal per RFC 1009. To quote: The interconnected LANs of an organization will be given the same network number but different subnet numbers. The distinction between the subnets of such a subnetted network must not be visible outside that network. Thus, wide-area routing in the rest of the Internet will be based only upon the part of the IP destination address; gateways outside the network will lump and together to form an uninterpreted "rest" part of the 32-bit IP address. The whole point of subnets is to provide a LAYERED, HEIRARCHICAL approach to routing. Anyone outside the subnetted network must be able to route solely on the basis of network number. Hosts on your network 128.5 cannot do this. Your configuration does not work because it is illegal. It is surely possible to envision all sorts of ways of "solving" this supposed problem. But then you will fail to solve the problem that subnetting was intended to solve. That problem was that routing at the upper (network) layer was overloading from too many networks. Subnets, by hiding a layer of the network topology, solved this. The restrctions of subnets are readily dealt with by proper (sub)network design. [The same approach was applied to DECnet in Phase IV, with areas. What you are asking for is the equivalent of allowing node 7.33 in DECnet to plopped down in the middle of area 5 and have it work.]