Re: [PATCH] IPv6: Allow Both IPv6 and IPv4 Sockets on the Same Port Number (IPV6_V6ONLY Support)

   From: Brad Hards [off-list ref]
   Date: Thu, 3 Oct 2002 18:55:11 +1000

   Assume B has two network interfaces (B1 and B2) on seperate IPv4 links (net1 
   and net2). Host A is on net1 and Host C is on net2. Assume that both Host A 
   and Host C have the same autoconf address. So IP address is not enough 
   information for Host B to use to determine which interface to use in order to 
   contact Host A (instead of Host C).
   
   If host B has socket binding on IP+port+local interface, it all works out.
   
You want SO_BINDTODEVICE, which we have.