bgpd: bgpd-set-v4-nexthop-for-v6-peering.patch

BGP: While advertising v4 prefixes over a v6 session, set the correct v4 nexthop.

ISSUE:

For an IPv6 peer, BGPd sets the local router-id as the next-hop's v4 address.
This is incorrect as the router-id may not be a valid next-hop to be included
in UPDATEs that contain v4 prefixes.

PATCH:

Set the v4 address in the next-hop field based on the interface that the
peering is on (directly connected interface or loopback).

Signed-off-by: Pradosh Mohapatra <pmohapat at cumulusnetworks.com>
Reviewed-by: Scott Feldman <sfeldma at cumulusnetworks.com>
Acked-by: Feng Lu <lu.feng@6wind.com>

bgpd/bgp_zebra.c

@@ -534,6 +534,25 @@ if_get_ipv6_local (struct interface *ifp, struct in6_addr *addr)
 }
 #endif /* HAVE_IPV6 */
 
+static int
+if_get_ipv4_address (struct interface *ifp, struct in_addr *addr)
+{
+  struct listnode *cnode;
+  struct connected *connected;
+  struct prefix *cp;
+
+  for (ALL_LIST_ELEMENTS_RO (ifp->connected, cnode, connected))
+    {
+      cp = connected->address;
+      if ((cp->family == AF_INET) && !ipv4_martian(&(cp->u.prefix4)))
+	  {
+	    *addr = cp->u.prefix4;
+	    return 1;
+	  }
+    }
+  return 0;
+}
+
 int
 bgp_nexthop_set (union sockunion *local, union sockunion *remote, 
 		 struct bgp_nexthop *nexthop, struct peer *peer)
@@ -592,8 +611,9 @@ bgp_nexthop_set (union sockunion *local, union sockunion *remote,
     {
       struct interface *direct = NULL;
 
-      /* IPv4 nexthop.  I don't care about it. */
-      if (peer->local_id.s_addr)
+      /* IPv4 nexthop. */
+      ret = if_get_ipv4_address(ifp, &nexthop->v4);
+      if (!ret && peer->local_id.s_addr)
 	nexthop->v4 = peer->local_id;
 
       /* Global address*/

lib/prefix.h

@@ -196,4 +196,14 @@ extern const char *inet6_ntoa (struct in6_addr);
 
 extern int all_digit (const char *);
 
+static inline int ipv4_martian (struct in_addr *addr)
+{
+  in_addr_t ip = addr->s_addr;
+
+  if (IPV4_NET0(ip) || IPV4_NET127(ip) || IPV4_CLASS_DE(ip)) {
+    return 1;
+  }
+  return 0;
+}
+
 #endif /* _ZEBRA_PREFIX_H */