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 <[email protected]>

Author: louis-6wind

bgpd/bgp_zebra.c

@@ -302,11 +302,12 @@ 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;
 
@@ -341,6 +342,23 @@ 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 (!IPV6_ADDR_SAME(&connected->address->u.prefix6,
+							    &peer->nexthop.v6_global))
+						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
@@ -351,9 +369,10 @@ 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)) ||
-			     IN6_IS_ADDR_LINKLOCAL(&peer->nexthop.v6_global))) {
+			if (v6_ll_in_nh_global ||
+			    (peer->conf_if && strcmp(peer->conf_if, ifc->ifp->name) == 0 &&
+			     (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, &peer->nexthop.v6_global, &addr->u.prefix6);