... and finally, we got a first working version of a dual-stack lwIP runnin IPv4 and IPv6 in parallel - big thanks to Ivan Delamer! (this is work in progress, so please beware, test a lot and report problems!)

src/netif/etharp.c

@@ -55,6 +55,7 @@
 #include "lwip/dhcp.h"
 #include "lwip/autoip.h"
 #include "netif/etharp.h"
+#include "lwip/ip6.h"
 
 #if PPPOE_SUPPORT
 #include "netif/ppp_oe.h"
@@ -1301,6 +1302,19 @@ ethernet_input(struct pbuf *p, struct netif *netif)
       break;
 #endif /* PPPOE_SUPPORT */
 
+#if LWIP_IPV6
+    case PP_HTONS(ETHTYPE_IPV6): /* IPv6 */
+      /* skip Ethernet header */
+      if(pbuf_header(p, -(s16_t)SIZEOF_ETH_HDR)) {
+        LWIP_ASSERT("Can't move over header in packet", 0);
+        goto free_and_return;
+      } else {
+        /* pass to IPv6 layer */
+        ip6_input(p, netif);
+      }
+      break;
+#endif /* LWIP_IPV6 */
+
     default:
       ETHARP_STATS_INC(etharp.proterr);
       ETHARP_STATS_INC(etharp.drop);

src/netif/ethernetif.c

@@ -51,8 +51,9 @@
 #include "lwip/mem.h"
 #include "lwip/pbuf.h"
 #include "lwip/sys.h"
-#include <lwip/stats.h>
-#include <lwip/snmp.h>
+#include "lwip/stats.h"
+#include "lwip/snmp.h"
+#include "lwip/ethip6.h"
 #include "netif/etharp.h"
 #include "netif/ppp_oe.h"
 
@@ -239,6 +240,7 @@ ethernetif_input(struct netif *netif)
   switch (htons(ethhdr->type)) {
   /* IP or ARP packet? */
   case ETHTYPE_IP:
+  case ETHTYPE_IPV6:
   case ETHTYPE_ARP:
 #if PPPOE_SUPPORT
   /* PPPoE packet? */
@@ -305,6 +307,9 @@ ethernetif_init(struct netif *netif)
    * from it if you have to do some checks before sending (e.g. if link
    * is available...) */
   netif->output = etharp_output;
+#if LWIP_IPV6
+  netif->output_ip6 = ethip6_output;
+#endif /* LWIP_IPV6 */
   netif->linkoutput = low_level_output;
   
   ethernetif->ethaddr = (struct eth_addr *)&(netif->hwaddr[0]);