bgpd: do not insert link-local with local unchanged

Do not add an IPv6 link-local nexthop if the originating peer does not
provide one and the nexthop-local unchanged setting is enabled.

Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>
(cherry picked from commit 34c1dd076e5f9ea2a7eb8820b204696dc692667d)

diff --git a/bgpd/bgp_route.c b/bgpd/bgp_route.c
index 18f1e5fd04364ad1250b0d637ced87b503fa27c5..b0f91b58b9c99f306dca897cffe5e4aa289a502f 100644 (file)
--- a/bgpd/bgp_route.c
+++ b/bgpd/bgp_route.c
@@ -2155,6 +2155,7 @@ bool subgroup_announce_check(struct bgp_dest *dest, struct bgp_path_info *pi,
        bool nh_reset = false;
        uint64_t cum_bw;
        mpls_label_t label;
+       bool global_and_ll = false;
 
        if (DISABLE_BGP_ANNOUNCE)
                return false;
@@ -2465,22 +2466,26 @@ bool subgroup_announce_check(struct bgp_dest *dest, struct bgp_path_info *pi,
         * we do not announce LL address as `::`.
         */
        if (NEXTHOP_IS_V6) {
-               attr->mp_nexthop_len = BGP_ATTR_NHLEN_IPV6_GLOBAL;
-               if ((CHECK_FLAG(peer->af_flags[afi][safi],
-                               PEER_FLAG_NEXTHOP_LOCAL_UNCHANGED)
-                    && IN6_IS_ADDR_LINKLOCAL(&attr->mp_nexthop_local))
-                   || (!reflect && !transparent
-                       && IN6_IS_ADDR_LINKLOCAL(&peer->nexthop.v6_local)
-                       && peer->shared_network
-                       && (from == bgp->peer_self
-                           || peer->sort == BGP_PEER_EBGP))) {
+               if (CHECK_FLAG(peer->af_flags[afi][safi], PEER_FLAG_NEXTHOP_LOCAL_UNCHANGED)) {
+                       /* nexthop local unchanged: only include the link-local nexthop if it
+                        * was already present.
+                        */
+                       if (IN6_IS_ADDR_LINKLOCAL(&attr->mp_nexthop_local))
+                               global_and_ll = true;
+               } else if (!reflect && !transparent &&
+                          IN6_IS_ADDR_LINKLOCAL(&peer->nexthop.v6_local) && peer->shared_network &&
+                          (from == bgp->peer_self || peer->sort == BGP_PEER_EBGP))
+                       global_and_ll = true;
+
+               if (global_and_ll) {
                        if (safi == SAFI_MPLS_VPN)
                                attr->mp_nexthop_len =
                                        BGP_ATTR_NHLEN_VPNV6_GLOBAL_AND_LL;
                        else
                                attr->mp_nexthop_len =
                                        BGP_ATTR_NHLEN_IPV6_GLOBAL_AND_LL;
-               }
+               } else
+                       attr->mp_nexthop_len = BGP_ATTR_NHLEN_IPV6_GLOBAL;
 
                /* Clear off link-local nexthop in source, whenever it is not
                 * needed to