Date: Tue, 15 Aug 2000 08:03:38 +0400 From: "Eugene Mogutov" <eugene_m@mail.ru> To: freebsd-net@freebsd.org Subject: Broadcast address and multihomed host Message-ID: <E13OXww-0008DB-00@f10.mail.ru>
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Hi Recently a friend of mine noticed that his FreeBSD router treats broadcast addresses of local subnets as local (i.e. as if they were addresses of router interfaces). A brief example: a multihomed host has a pair of interfaces, their addresses are aa.aa.aa.1/24 and bb.bb.bb.1/24, where /24 stands for netmask corresponding to Class C. It is possible to establish tcp connection to our host using destination address bb.bb.bb.255 (broadcast address for local subnet connected to interface bb.bb.bb.1), it is required, however, that those tcp packets pass via interface aa.aa.aa.1. The same story is about connecting to aa.aa.aa.255 from the host reachable via interface bb.bb.bb.1. Only 'all ones' broadcast address does the trick, 'all zeroes' doesn't. If I'm not mistaken at least 2.2.6, 3.3 and 3.4 behave so. It seems that packet filter rulesets (e.g. those of ipfw) using specific addresses of multihomed host's interfaces to restrict access to services running on that host can be easily overriden by using broadcast addresses. Is it a feature of BSD stack (I haven't seen it neither on linux 2.2.x, nor on 2.0.x) ? If it is, is there a way to disable it? Thanks, eugene To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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