This patch fixes the nexthop used when transporting IPv4 routes over an
IPv6 BGP peering. Previously, the bgp router id was used; with this patch,
the lowest IP from the interface is used.

Patch by David Lamparter <equinox-quagga@diac24.net>, 2007-02-23

--- quagga/bgpd/bgp_zebra.c.orig	2006-11-30 17:36:57.000000000 +0100
+++ quagga/bgpd/bgp_zebra.c	2007-02-23 04:01:51.456015851 +0100
@@ -432,6 +432,28 @@
   return NULL;
 }
 
+static int
+if_get_ipv4 (struct interface *ifp, struct in_addr *addr)
+{
+  struct listnode *cnode;
+  struct connected *connected;
+  struct prefix *cp; 
+  int hit = 0;
+  
+  for (ALL_LIST_ELEMENTS_RO (ifp->connected, cnode, connected))
+    {
+      cp = connected->address;
+	    
+      if (cp->family == AF_INET)
+	if (!hit || ntohl(cp->u.prefix4.s_addr) < ntohl(addr->s_addr))
+	  {
+	    memcpy (addr, &cp->u.prefix4, IPV4_MAX_BYTELEN);
+	    hit = 1;
+	  }
+    }
+  return hit;
+}
+
 #ifdef HAVE_IPV6
 struct interface *
 if_lookup_by_ipv6 (struct in6_addr *addr)
@@ -586,7 +608,8 @@
       struct interface *direct = NULL;
 
       /* IPv4 nexthop.  I don't care about it. */
-      if (peer->local_id.s_addr)
+      ret = if_get_ipv4 (ifp, &nexthop->v4);
+      if (!ret && peer->local_id.s_addr)
 	nexthop->v4 = peer->local_id;
 
       /* Global address*/