Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!ucbvax!UC.MSC.UMN.EDU!slevy From: slevy@UC.MSC.UMN.EDU ("Stuart Levy") Newsgroups: comp.protocols.tcp-ip Subject: Re: Subnetting Message-ID: <8805110351.AA05761@uc.msc.umn.edu> Date: 11 May 88 03:51:40 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 18 It looks as though 4.3BSD subnetting code doesn't store a net mask per route. There's a net mask per -interface-, but it doesn't seem to be used the way you'd hope. There's effectively just one subnet mask per net for routing purposes (I think it uses the mask set by the first interface on the net) -- that is, 4.3BSD silently assumes equal-sized subnets on a given net. If I say ifconfig ex0 128.101.1.2 netmask 255.255.255.0 ifconfig ex1 128.101.27.27 netmask 255.255.240.0 the interface route for ex1 has a destination address of "128.101.16.0" (reasonable) BUT the route is only used when sending to 128.101.16.anything. Sending to 128.101.17.anything, ..., 128.101.31.anything does not increment the interface route's usage count. 4.3's multiple subnet masks are meaningful for interfaces on different nets but not for variable-sized subnets on a single net. It'll be interesting to see whether SUN 4.0 works the same way.