bgpd: fix sending ipv6 local nexthop if global present

bgpd keeps on advertising IPv6 prefixes with a IPv6 link-local nexthop
after a valid IPv6 global appears.

At bgpd startup, the IPv6 global is announced by zebra after the
link-local. Only the link-local is advertised. Clearing the BGP sessions
make the global to to be announced.

Update the nexthops with the global IPv6 when available.

Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>

bgpd/bgp_zebra.c

@@ -303,11 +303,12 @@ static int bgp_ifp_down(struct interface *ifp)
 
 static int bgp_interface_address_add(ZAPI_CALLBACK_ARGS)
 {
-	struct connected *ifc;
+	struct connected *ifc, *connected;
 	struct bgp *bgp;
 	struct peer *peer;
 	struct prefix *addr;
 	struct listnode *node, *nnode;
+	bool v6_ll_in_nh_global;
 	afi_t afi;
 	safi_t safi;
 
@@ -340,6 +341,30 @@ static int bgp_interface_address_add(ZAPI_CALLBACK_ARGS)
 			addr = ifc->address;
 
 			for (ALL_LIST_ELEMENTS(bgp->peer, node, nnode, peer)) {
+				v6_ll_in_nh_global = false;
+
+				if (IN6_IS_ADDR_LINKLOCAL(
+					    &peer->nexthop.v6_global)) {
+					frr_each (if_connected,
+						  ifc->ifp->connected,
+						  connected) {
+						if (connected->address->family !=
+						    AF_INET6)
+							continue;
+						if (memcmp(&connected->address
+								    ->u.prefix6,
+							   &peer->nexthop.v6_global,
+							   IPV6_MAX_BYTELEN) !=
+						    0)
+							continue;
+						/* peer->nexthop.v6_global contains a link-local address
+						 * that needs to be replaced by the global address.
+						 */
+						v6_ll_in_nh_global = true;
+						break;
+					}
+				}
+
 				/*
 				 * If the Peer's interface name matches the
 				 * interface name for which BGP received the
@@ -350,14 +375,13 @@ static int bgp_interface_address_add(ZAPI_CALLBACK_ARGS)
 				 * into peer's v6_global and send updates out
 				 * with new nexthop addr.
 				 */
-				if ((peer->conf_if &&
-				     (strcmp(peer->conf_if, ifc->ifp->name) ==
-				      0)) &&
-				    ((IS_MAPPED_IPV6(
-					     &peer->nexthop.v6_global)) ||
+				if (((peer->conf_if &&
+				      (strcmp(peer->conf_if, ifc->ifp->name) ==
+				       0)) ||
+				     v6_ll_in_nh_global) &&
+				    ((IS_MAPPED_IPV6(&peer->nexthop.v6_global)) ||
 				     IN6_IS_ADDR_LINKLOCAL(
 					     &peer->nexthop.v6_global))) {
-
 					if (bgp_debug_zebra(ifc->address)) {
 						zlog_debug("Update peer %pBP's current intf global addr from %pI6 to %pI6 and send updates",
 							   peer,