Relax the list of interfaces which support IPv6 a bit.

No longer require IFF_MULTICAST for all interfaces. It is save to skip
this for interfaces that don't require a ND cache. Also do not assign a
link-local address in such cases. This affects point-to-point interfaces
and the NBMA / point-to-multipoint interfaces like mpe(4), mgre(4) and wg(4).
The NBMA interfaces need some alternative way to figure out the address
mapping. In the end this allows non-multicast interfaces to work with IPv6.
OK dlg@ kn@

diff --git a/sys/netinet6/in6_ifattach.c b/sys/netinet6/in6_ifattach.c
index 09a9878..7550297 100644 (file)
--- a/sys/netinet6/in6_ifattach.c
+++ b/sys/netinet6/in6_ifattach.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: in6_ifattach.c,v 1.119 2022/09/08 10:22:07 kn Exp $   */
+/*     $OpenBSD: in6_ifattach.c,v 1.120 2022/11/14 17:12:55 claudio Exp $      */
 /*     $KAME: in6_ifattach.c,v 1.124 2001/07/18 08:32:51 jinmei Exp $  */
 
 /*
@@ -373,7 +373,7 @@ in6_ifattach(struct ifnet *ifp)
        if (ifp->if_mtu < IPV6_MMTU)
                return (EINVAL);
 
-       if ((ifp->if_flags & IFF_MULTICAST) == 0)
+       if (nd6_need_cache(ifp) && (ifp->if_flags & IFF_MULTICAST) == 0)
                return (EINVAL);
 
        /*
@@ -389,12 +389,12 @@ in6_ifattach(struct ifnet *ifp)
                        return (error);
        }
 
-       /* Interfaces that rely on strong a priori cryptographic binding of
-        * IP addresses are incompatible with automatically assigned llv6. */
-       switch (ifp->if_type) {
-       case IFT_WIREGUARD:
+       /*
+        * Only interfaces that need the ND cache should automatically
+        * assign a link local address.
+        */
+       if (!nd6_need_cache(ifp))
                return (0);
-       }
 
        /* Assign a link-local address, if there's none. */
        if (in6ifa_ifpforlinklocal(ifp, 0) == NULL) {