Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!rutgers!ames!sdcsvax!ucbvax!GVAX.CS.CORNELL.EDU!jqj From: jqj@GVAX.CS.CORNELL.EDU (J Q Johnson) Newsgroups: comp.protocols.tcp-ip Subject: Re: How do you break up a B class number? Message-ID: <8707311830.AA27720@gvax.cs.cornell.edu> Date: Fri, 31-Jul-87 14:30:06 EDT Article-I.D.: gvax.8707311830.AA27720 Posted: Fri Jul 31 14:30:06 1987 Date-Received: Sun, 2-Aug-87 01:56:07 EDT References: <8346@cornell.UUCP> Sender: daemon@ucbvax.BERKELEY.EDU Reply-To: jqj@gvax.cs.cornell.edu (J Q Johnson) Distribution: world Organization: Cornell Univ. CS Dept, Ithaca NY Lines: 19 Dan Lynch suggests (in jest, I think) a solution to the heterogenous subnet problem: > . . . have more than one entwork number on the same "cable"! So break >the 16 bits up into 256 nets of 256 hosts and assign 4 of the to the >main cable. It's legal , but wil it work!? No, it probably won't work. One big problem is that you are likely to have broadcasts with all sorts of broadcast addresses. Suppose that we have 128.84.253.0 and 128.84.33.0 (netmask 0xffffff00) on the same cable. Then the host with interface address 128.84.253.3 will occasionally receive Ethernet broadcasts that contain IP broadcasts with destination 128.84.33.255. If this is a typical 4.3BSD implementation, it will say "that's not a broadcast address, so I gotta forward or send an ICMP unreachable or something". Result: every host on 128.84.253.0 replies at the same time, and you get a big Ethernet collision. We tried something like this, and sure enough our SUNs were reporting 70% collision rates! Another version of the Ethernet meltdown Charles Hedrick so aptly described in these pages a few weeks ago.