bgpd: Default route gets withdrawn from peer when default-originate i…

…s configured

      When static default route is present in RIB and advertised to peer,
      configuring default-originate for that peer results in withdrawal
      of the route.

      Fix :
      Delete the adj-out entry for the previously advertised static
      default route without sending withdraw message and then
      advertise default route with the attribute BGP_ORIGIN_IGP
      Checks are added in bgp_adj_out_unset_subgroup() and
      subgroup_announce_table() to verify if default originate is enabled
      and suppress the explicit withdraw message which causes default route
      withdraw from the peer router.

Signed-off-by: kssoman <somanks@gmail.com>

bgpd/bgp_updgrp_adv.c

@@ -533,6 +533,15 @@ void bgp_adj_out_unset_subgroup(struct bgp_node *rn,
 		if (adj->adv)
 			bgp_advertise_clean_subgroup(subgrp, adj);
 
+		/* If default originate is enabled and the route is default
+		 * route, do not send withdraw. This will prevent deletion of
+		 * the default route at the peer.
+		 */
+		if (CHECK_FLAG(subgrp->sflags,
+			       SUBGRP_STATUS_DEFAULT_ORIGINATE) &&
+		    is_default_prefix(&rn->p))
+			return;
+
 		if (adj->attr && withdraw) {
 			/* We need advertisement structure.  */
 			adj->adv = bgp_advertise_new();
@@ -636,12 +645,25 @@ void subgroup_announce_table(struct update_subgroup *subgrp,
 							    rn_p, &attr))
 					bgp_adj_out_set_subgroup(rn, subgrp,
 								 &attr, ri);
-				else
+				else {
+					/* If default originate is enabled for
+					 * the peer, do not send explicit
+					 * withdraw. This will prevent deletion
+					 * of default route advertised through
+					 * default originate
+					 */
+					if (CHECK_FLAG(
+					    peer->af_flags[afi][safi],
+					    PEER_FLAG_DEFAULT_ORIGINATE) &&
+						is_default_prefix(&rn->p))
+						break;
+
 					bgp_adj_out_unset_subgroup(
 						rn, subgrp, 1,
 						bgp_addpath_id_for_peer(
 							peer, afi, safi,
 							&ri->tx_addpath));
+				}
 			}
 	}
 
@@ -709,7 +731,9 @@ void subgroup_default_originate(struct update_subgroup *subgrp, int withdraw)
 	struct prefix p;
 	struct peer *from;
 	struct bgp_node *rn;
+	struct bgp_path_info *pi;
 	struct peer *peer;
+	struct bgp_adj_out *adj;
 	route_map_result_t ret = RMAP_DENYMATCH;
 	afi_t afi;
 	safi_t safi;
@@ -779,20 +803,42 @@ void subgroup_default_originate(struct update_subgroup *subgrp, int withdraw)
 	}
 
 	if (withdraw) {
+		/* Withdraw the default route advertised using default
+		 * originate
+		 */
 		if (CHECK_FLAG(subgrp->sflags, SUBGRP_STATUS_DEFAULT_ORIGINATE))
 			subgroup_default_withdraw_packet(subgrp);
 		UNSET_FLAG(subgrp->sflags, SUBGRP_STATUS_DEFAULT_ORIGINATE);
+
+		/* Check if the default route is in local BGP RIB which is
+		 * installed through redistribute or network command
+		 */
+		memset(&p, 0, sizeof(p));
+		p.family = afi2family(afi);
+		p.prefixlen = 0;
+
+		/* If default route is present in the local RIB, advertise the
+		 * route
+		 */
+		rn = bgp_afi_node_lookup(bgp->rib[afi][safi], afi, safi, &p, NULL);
+		if (rn != NULL) {
+			for (pi = bgp_node_get_bgp_path_info(rn); pi;
+			     pi = pi->next) {
+				if (CHECK_FLAG(pi->flags, BGP_PATH_SELECTED))
+					if (subgroup_announce_check(rn, pi,
+								    subgrp,
+								    &rn->p,
+								    &attr))
+						bgp_adj_out_set_subgroup(rn,
+									 subgrp,
+									 &attr,
+									 pi);
+			}
+		}
 	} else {
 		if (!CHECK_FLAG(subgrp->sflags,
 				SUBGRP_STATUS_DEFAULT_ORIGINATE)) {
 
-			if (CHECK_FLAG(bgp->flags, BGP_FLAG_GRACEFUL_SHUTDOWN))
-				bgp_attr_add_gshut_community(new_attr);
-
-			SET_FLAG(subgrp->sflags,
-				 SUBGRP_STATUS_DEFAULT_ORIGINATE);
-			subgroup_default_update_packet(subgrp, new_attr, from);
-
 			/* The 'neighbor x.x.x.x default-originate' default will
 			 * act as an
 			 * implicit withdraw for any previous UPDATEs sent for
@@ -806,9 +852,36 @@ void subgroup_default_originate(struct update_subgroup *subgrp, int withdraw)
 
 			rn = bgp_afi_node_get(bgp->rib[afi][safi], afi, safi,
 					      &p, NULL);
-			bgp_adj_out_unset_subgroup(
-				rn, subgrp, 0,
+			if (rn == NULL)
+				return;
+
+			/* Remove the adjacency for the previously advertised
+			 * default route
+			 */
+			adj = adj_lookup(rn, subgrp,
 				BGP_ADDPATH_TX_ID_FOR_DEFAULT_ORIGINATE);
+			if (adj != NULL) {
+				/* Clean up previous advertisement.  */
+				if (adj->adv)
+					bgp_advertise_clean_subgroup(subgrp,
+								     adj);
+
+				/* Remove  from adjacency. */
+				RB_REMOVE(bgp_adj_out_rb, &rn->adj_out, adj);
+
+				/* Free allocated information.  */
+				adj_free(adj);
+
+				bgp_unlock_node(rn);
+			}
+
+			/* Advertise the default route */
+			if (CHECK_FLAG(bgp->flags, BGP_FLAG_GRACEFUL_SHUTDOWN))
+				bgp_attr_add_gshut_community(new_attr);
+
+			SET_FLAG(subgrp->sflags,
+				 SUBGRP_STATUS_DEFAULT_ORIGINATE);
+			subgroup_default_update_packet(subgrp, new_attr, from);
 		}
 	}