title: how to determine value for ipv6mr_interface field of ipv6_mreq structure
body: <p>I am trying to create a BSD socket to listen for messages from a specific IPv6 multicast address.  I currently have no problem creating the socket listening on the correct address 0::0.</p>
  
  <p>The problem is that I am running on a small embedded linux server with multiple NICs; here the ipv6mr_interface field of the ipv6_mreq is important.  By trial and error, I have determined that 0, 1 and 3 do not work, but 2, does (it gives me all IPv6 multicast messages to my address, ff05::3, arriving on the correct interface).</p>
  
  <p>My question is: How do I correlate, in linux, my interface, whos' address I know, to the correct interface number?</p>