6to4 support

[Roger Venning <r.venning@xxxxxxxxxxx>]

Greetings all,

attached is a patch to provide 6to4 support for Linux. This allows for 
connection to the mbone without statically configured tunnels.

6to4 provides a mechanism for IPv6 tunneling through IPv4 domains using IPv4 
addresses embedded in site prefixes.

Further details can be found in on a webpage containing a description and 
configuration information at http://www.users.bigpond.com/r.venning/, or at 
http://www.ietf.org/internet-drafts/draft-ietf-ngtrans-6to4-07.txt

The patch is to sit.c, and simply provides another check in addition to the 
current support for compatibility mode addresses when the sit0 device has 
wildcard remote and local addresses.

A synopsis of configuration

IP=<insert global scope IP address belonging to your 6to4 gateway>
quads=`echo ${IP} | sed 's/\./ /g'`
prefix=`printf "2002:%x%x:%x%x\n" ${quads}`
ip link set sit0 up     # we want sit0 running in wildcard send/receive mode
ip addr add ${prefix}::1 dev sit0    # simplest case...
ip route add 2002::/16 dev sit0     # route to 6to4 land via sit0
ip route add ::/0 via ::131.107.65.121 # I use microsoft's 6to4 site
                                    # you might be able to use 
ipv6-router.cisco.com
                                    # point is, use somebody as gateway to 6bone

Other IPv6 hosts on the site can then proceed to use the global scope
prefix 2002:...:....::/48

cheers,

Roger.



--- linux-2.4.0-test6clean/net/ipv6/sit.c       Sat Aug  5 11:18:49 2000
+++ linux-2.4.0-test6hacked/net/ipv6/sit.c      Mon Aug 28 08:43:49 2000
@@ -27,6 +27,7 @@
 #include <linux/netdevice.h>
 #include <linux/if_arp.h>
 #include <linux/icmp.h>
+#include <linux/inet.h>
 #include <asm/uaccess.h>
 #include <linux/init.h>
 #include <linux/netfilter_ipv4.h>
@@ -55,6 +56,7 @@
 
 #define HASH_SIZE  16
 #define HASH(addr) ((addr^(addr>>4))&0xF)
+#define SIXTO4PREF htons(0x2002)
 
 static int ipip6_fb_tunnel_init(struct net_device *dev);
 static int ipip6_tunnel_init(struct net_device *dev);
@@ -420,6 +422,28 @@
        return ip_send(skb);
 }
 
+
+/* returns the embedded IPv4 address if the IPv6 address
+   comes from 6to4 (draft-ietf-ngtrans-6to4-06) addr space */
+static inline u32 try_6to4(struct in6_addr *v6dst) {
+       u32 dst = 0;
+       
+       if (*v6dst->s6_addr16 == SIXTO4PREF) {
+               /* 6to4 v6 addr has 16 bits prefix, 32 v4addr, 16 SLA, ... */
+               memcpy(&dst, &v6dst->s6_addr16[1], sizeof(u32));
+               if (IN_MULTICAST(ntohl(dst)) || 
+                  (dst == htonl(INADDR_BROADCAST)) ||
+                  IN_LOOPBACK(ntohl(dst))) {
+                       if (net_ratelimit())
+                               printk("sit.c: 6to4 IPv6 dest. encoded naughty 
IPv4 dest. %s\n",
+                                      in_ntoa(dst));
+                       return 0;
+               }
+       }
+       return dst;
+}
+
+
 /*
  *     This function assumes it is being called from dev_queue_xmit()
  *     and that skb is filled properly by that function.
@@ -448,6 +472,12 @@
 
        if (skb->protocol != __constant_htons(ETH_P_IPV6))
                goto tx_error;
+
+       if (!dst) {
+               /* well we first check if they are using the SIT device
+                  in wildcard 6to4 send mode */
+               dst = try_6to4(&iph6->daddr);
+       }
 
        if (!dst) {
                struct neighbour *neigh = NULL;