Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!bu.edu!snorkelwacker!bloom-beacon!eru!hagbard!sunic!mcsun!ukc!mucs!logitek!martino From: martino@logitek.co.uk (Martin O'Nions) Newsgroups: comp.protocols.tcp-ip Subject: Re: Multiple subnets on same cable Keywords: subnet IP ICMP fnord Message-ID: Date: 12 Nov 90 10:00:29 GMT References: Organization: Logitek Plc. Lines: 32 freiss@nixdorf.de (the hacker) writes: >This might be a silly question, but it's been worrying me for some time. >What happens if different IP subnets live on the same ethernet cable? >I'm worried about excessive ICMP traffic (ICMP net_redirect packets); >I see some SGI workstations here react to some packets from a >different subnet with this ICMP message. >Could somebody tell me if this is a problem or what other >problems I haven't even thought of might arise? >Pointers to books, RFCs etc. on this subject are also welcome. Observe caution! RFC950 adds a couple of new ICMP types, including one to allow determination of subnet mask for this segment. This specifically states that a host may request the active subnet mask EVEN IF IT DOES NOT KNOW ITS OWN IP ADDRESS (IP 0.0.0.0 (!?**@!)). Therefore, even though it it is (hopefully) unlikely to occur, this section of the specification could cause prob's if someone chose to implement the RFC in this detail. (P.S. If anyone has any info. which updates/obsoletes/contradicts this, don't flame me - mail me!) -- +------------------------------------------------+-----------------------+ | I've got a little black book with my poems in, | Martin O'Nions | | I've got a bag with a toothbrush and a comb in,| Logitek Group Support | | When I'm a good dog they sometimes throw me a | martino@logitek.co.uk | | bone in (Roger Waters - The Wall) | 0257 426 644 | +------------------------------------------------+-----------------------+