On Wed, Feb 20, 2013 at 12:36:13AM -0600, Todd T. Fries wrote:
> The source address selection mechanism in IPv4 is to my understanding:
>
> the first address on the interface associated with the route
> to the remote host
>
> The source address selection mechanism in IPv6 is to my understanding:
>
> for each of the global addresses on a system, turn it into an integer
> and subtract it from the destination address. The difference closest
> to zero decides what address will be selected because it is 'closest'.
>
> Personally I'd be happy if IPv6 mimicked IPv4 in this regard. Other OS's
> permit configurable address selection criteria in the kernel, but I'll be
> the first to suggest this is not the OpenBSD way. The default should be
> good enough and .. this is not good enough for me in every scenario I've
> encountered it.
I am running with this diff for a while now. It gives the outgoing
interface a higher priority when selecting an IPv6 source addresse.
More and more RFCs on that topic get published, making things more
complicated. I am not convinced that this diff is good solution
in general.
bluhm
Index: netinet6/in6.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet6/in6.c,v
retrieving revision 1.101
diff -u -p -r1.101 in6.c
--- netinet6/in6.c 30 Nov 2012 13:48:12 -0000 1.101
+++ netinet6/in6.c 3 Feb 2013 12:09:31 -0000
@@ -2263,6 +2263,12 @@ in6_ifawithscope(struct ifnet *oifp, str
IN6_IFF_DEPRECATED) == 0)
goto replace;
+ /* RFC 3484 5. Rule 5: Prefer outgoing interface */
+ if (ifa_best->ia_ifp == oifp && ifp != oifp)
+ continue;
+ if (ifa_best->ia_ifp != oifp && ifp == oifp)
+ goto replace;
+
/*
* At this point, we have two cases:
* 1. we are looking at a non-deprecated address,
