From owner-freebsd-hackers  Tue Aug 26 07:02:18 1997
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To: Aled Morris <aledm@routers.co.uk>
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From: "Louis A. Mamakos" <louie@TransSys.COM>
Subject: Re: UDP "to" address? 
References: <Pine.BSF.3.91.970826134032.21490D-100000@ns.uk.peer.net> 
In-reply-to: Your message of "Tue, 26 Aug 1997 13:42:45 BST."
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Date: Tue, 26 Aug 1997 09:52:07 -0400
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Typically, a portable approach to doing this is to create a socket
per interface address and bind it.  Then you look at which fd the
packet was received on to determine the destination address.

Look at named and xntpd to get a sense of this.  In fact, you can
probably steal a lot of this code and apply it directly.  

There also seems to be a socket option you can set which returns the
destination address in the "control information" field specified
with recvmsg(2).   I noticed the code for this in ip_input.c.

louie