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To: "Randall R. Stewart (home)" <randall@stewart.chicago.il.us>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Mon, 19 Jan 2004 06:13:25 CST."
             <400BC9E5.8010609@stewart.chicago.il.us> 
Date: Mon, 19 Jan 2004 13:30:18 +0100
Message-ID: <92687.1074515418@critter.freebsd.dk>
cc: net@freebsd.org
Subject: Re: Multihomed UDP server 
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In message <400BC9E5.8010609@stewart.chicago.il.us>, "Randall R. Stewart (home)
" writes:
>>>On Mon, 19 Jan 2004, 12:07+0100, Poul-Henning Kamp wrote:

>>>>Simple question:
>>>>
>>>>Very simple UDP server daemon.
>>>>
>>>>Many clients (connect(2)'ing a socket for each is not an option)
>>>>
>>>>Multihomed machine.
>>>>
>>>>What's the simple trick to replying with the same source-IP as the
>>>>client used as destination-IP ?
>>
>>I'm considering ways to make sendmsg(2)/recvmsg(2) DTRT, and my
>>current candidate is give them a flag bit which says "msg_name has
>>both addresses".

Following the code it seems that it is in fact possible to do with
sendmsg(2)/recvmsg(2) already, and my test shows that at least the
receive side works.

I challenge anybody to point out where this is mentioned in the docs,
and once people give up I'll tell how to do it :-)

>Poul:
>
>One of the problems I think that is fundamental to BSD and
>multi-homing is the lack of supports for multiple-default routes.

I agree.


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.