First of all thank you for you reply !

On 09/22/2013 10:07 AM, Francis Dupont via RT wrote:
> On Thu Sep 12 15:56:23 2013, jpopelka@redhat.com wrote:
>
> => a simple question: is the problem for multicast or
> unicast packets (it should work for multicast packets
> but for unicast packets it has no chance to work with
> a single global socket bound to *.port)?

Unicast I think - I've seen it with Reply in response to Renew/Rebind 
and on other machine (kernel) with Advertise.

> => local_address* is for agents (i.e., relays and servers).
> In fact this part of the code is essentially for agents.
>
>> I don't know the internals, so the patch can be completely wrong
>> but up to now it's seemed to fix the problem and not cause any others.
>> I'll update it if I find something better.
>
> => I am afraid it will break agents via the multicast receive.

We already dropped it and have been using the following, i.e. binding to 
interface even for AF_INET6:

+++ dhcp-4.2.5/common/socket.c @@ -245,7 +245,7 @@ 
if_register_socket(struct interface_info

  #if defined(SO_BINDTODEVICE)
  	/* Bind this socket to this interface. */
-	if ((local_family != AF_INET6) && (info->ifp != NULL) &&
+	if (((do_multicast == 0)||(*do_multicast == 0)) && (info->ifp != NULL) &&
  	    setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
  			(char *)(info -> ifp), sizeof(*(info -> ifp))) < 0) {
  		log_fatal("setsockopt: SO_BINDTODEVICE: %m");




regards,
Jiri