Date: Mon, 13 Dec 1999 10:08:51 -0500 From: Mitch Collinsworth <mkc@Graphics.Cornell.EDU> To: Rhys Arkins <s350738@student.uq.edu.au> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: multihomed hosts Message-ID: <199912131508.KAA24545@benge.graphics.cornell.edu> In-Reply-To: Message from Rhys Arkins <s350738@student.uq.edu.au> of "Mon, 13 Dec 1999 14:33:58 %2B1000." <Pine.OSF.4.10.9912131416260.9198-100000@student.uq.edu.au>
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>Mitch, > >I have a question in regard to a reply you gave to a freeBSD networking >question. The question was: > >A) if the request comes in on one feed the reply goes out the same. > >Your reply was: > >Option A is not how IP works. At each hop, the path taken by a >packet is based on it's destination address and that host's or >router's current routing tables. There is no decision point based >on the route taken in the opposite direction. Your reply path will >be based on the destination address and the routing table at each >hop along the way, including your web server. > >I have been reading RFC 1122 and had been optimistic of being able to >achieve this until reading your reply. I was hoping you might know some >details of how the networking is done in freeBSD. Essentially what I need >is a "strong end system model" (Stevens) or the "strong ES model" (RFC >1122). Under a strong model, routing is effectively decided on the source >machine based upon the source address, not just the destination address. > >Taken from RFC 1122: >#------- > (A) A host MAY silently discard an incoming datagram whose > destination address does not correspond to the physical > interface through which it is received. > (B) A host MAY restrict itself to sending (non-source- > routed) IP datagrams only through the physical > interface that corresponds to the IP source address of > the datagrams. >#------- > >For a strong model, MAY is replaced with MUST. As long as an application >sets the source IP of packets to be the same as the destination IP of the >received packets, then data should theoretically go out the same interface >it came in. > >Do you know whether freeBSD uses the weak or strong model, and if it uses >the weak have you any idea how much modification would be necessary to >change it? > >thanks for your help, > >Rhys Arkins. Hi Rhys, It sounds like what you are talking about here is a host with multiple IP addresses. I don't fully recall the original discussion but I don't believe that was the case there. Certainly if you are using multiple addresses you have the possibility of making the initial routing decision based on source address. But this is not something I have any experience or knowledge of. Best bet for this sort of question is to post it to freebsd-questions (where I've cc-d this reply) or freebsd-net. -Mitch To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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