From: "Nitsche, Elia" <elia.nitsche@tuwien.ac.at>
Subject: Re: IPv4 route with IPv6 gateway
To: "tech@openbsd.org" <tech@openbsd.org>
Date: Mon, 14 Sep 2026 09:23:07 +0000

Hello,

what would make this diff merge able?

elia

Index: net/if.c
===================================================================
RCS file: /cvs/src/sys/net/if.c,v
diff -u -p -u -r1.763 if.c
--- net/if.c    22 Mar 2026 23:14:00 -0000    1.763
+++ net/if.c    15 Aug 2026 12:38:48 -0000
@@ -928,8 +928,13 @@ if_output_tso(struct ifnet *ifp, struct
 {
     uint32_t ifcap;
     int error;
+    sa_family_t af;
+    if (rt != NULL)
+        af = rt_key(rt)->sa_family;
+    else
+        af = dst->sa_family;

-    switch (dst->sa_family) {
+    switch (af) {
     case AF_INET:
         ifcap = IFCAP_TSOv4;
         break;
@@ -953,7 +958,7 @@ if_output_tso(struct ifnet *ifp, struct
         return error;

     if ((*mp)->m_pkthdr.len <= mtu) {
-        switch (dst->sa_family) {
+        switch (af) {
         case AF_INET:
             in_hdr_cksum_out(*mp, ifp);
             in_proto_cksum_out(*mp, ifp);
Index: net/if_ethersubr.c
===================================================================
RCS file: /cvs/src/sys/net/if_ethersubr.c,v
diff -u -p -u -r1.308 if_ethersubr.c
--- net/if_ethersubr.c    19 Dec 2025 02:04:13 -0000    1.308
+++ net/if_ethersubr.c    15 Aug 2026 12:38:48 -0000
@@ -220,9 +220,15 @@ ether_resolve(struct ifnet *ifp, struct
     struct rtentry *rt, struct ether_header *eh)
 {
     struct arpcom *ac = (struct arpcom *)ifp;
-    sa_family_t af = dst->sa_family;
     int error = 0;

+    sa_family_t af;
+    if (rt != NULL)
+        af = rt_key(rt)->sa_family;
+    else
+        // fallback
+        af = dst->sa_family;
+
     if (!ISSET(ifp->if_flags, IFF_RUNNING))
         senderr(ENETDOWN);

@@ -237,12 +243,24 @@ ether_resolve(struct ifnet *ifp, struct
     }
 #endif

+    /* packet type depends on af of rt->rt_dst (this might get overwritten later) */
     switch (af) {
     case AF_INET:
+        eh->ether_type = htons(ETHERTYPE_IP);
+        break;
+#ifdef INET6
+    case AF_INET6:
+        eh->ether_type = htons(ETHERTYPE_IPV6);
+        break;
+#endif
+    }
+
+    /* resolve LL depending on the af of dst */
+    switch (dst->sa_family) {
+    case AF_INET:
         error = arpresolve(ifp, rt, m, dst, eh->ether_dhost);
         if (error)
             return (error);
-        eh->ether_type = htons(ETHERTYPE_IP);

         /*
          * If broadcasting on a simplex interface, loopback a copy.
@@ -265,7 +283,6 @@ ether_resolve(struct ifnet *ifp, struct
         error = nd6_resolve(ifp, rt, m, dst, eh->ether_dhost);
         if (error)
             return (error);
-        eh->ether_type = htons(ETHERTYPE_IPV6);
         break;
 #endif
 #ifdef MPLS
Index: netinet/in.h
===================================================================
RCS file: /cvs/src/sys/netinet/in.h,v
diff -u -p -u -r1.149 in.h
--- netinet/in.h    2 Mar 2025 21:28:32 -0000    1.149
+++ netinet/in.h    15 Aug 2026 12:38:48 -0000
@@ -238,6 +238,7 @@ struct in_addr {

 #define    INADDR_ANY        __IPADDR(0x00000000)
 #define    INADDR_LOOPBACK        __IPADDR(0x7f000001)
+#define    INADDR_DUMMY        __IPADDR(0xc0000008)    /* 192.0.0.8 (RFC 7600) */
 #define    INADDR_BROADCAST    __IPADDR(0xffffffff)    /* must be masked */
 #ifndef _KERNEL
 #define    INADDR_NONE        __IPADDR(0xffffffff)    /* -1 return */
Index: netinet/ip_output.c
===================================================================
RCS file: /cvs/src/sys/netinet/ip_output.c,v
diff -u -p -u -r1.419 ip_output.c
--- netinet/ip_output.c    17 Jul 2026 18:51:29 -0000    1.419
+++ netinet/ip_output.c    15 Aug 2026 12:38:48 -0000
@@ -218,6 +218,9 @@ reroute:
         /* Set the source IP address */
         if (ip->ip_src.s_addr == INADDR_ANY && ia)
             ip->ip_src = ia->ia_addr.sin_addr;
+        /* if ia has not set an address */
+        if (ip->ip_src.s_addr == INADDR_ANY)
+            ip->ip_src.s_addr = INADDR_DUMMY;
     }

 #ifdef IPSEC