bgpd: allow routes to be imported if the ES/ES-VRF is not present

In a sym-IRB setup the remote ES may not be installed if the tenant
VRF is not present locally. To allow that case while retaining the
fast-failover benefits for the case where the tenant VRF is locally
present we use the following approach -
1. If ES is present in the tenant VRF we use the L3NHG for installing
the MAC-IP based tenant route. This allows for efficient failover via
L3NHG updates.
2. If the ES is not present locally in the corresponding tenant VRF we
fall back to a non-NHG multi-path based routing approach. In this
case individual routes are updated when the ES links flap.

PS: #1 can be turned off entirely by disabling use-l3-nhg in BGP.

Ticket: CM-30935

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>

bgpd/bgp_evpn.c

@@ -2852,7 +2852,8 @@ static int bgp_evpn_route_rmac_self_check(struct bgp *bgp_vrf,
 
 /* don't import hosts that are locally attached */
 static inline bool
-bgp_evpn_skip_vrf_import_of_local_es(const struct prefix_evpn *evp,
+bgp_evpn_skip_vrf_import_of_local_es(struct bgp *bgp_vrf,
+				     const struct prefix_evpn *evp,
 				     struct bgp_path_info *pi, int install)
 {
 	esi_t *esi;
@@ -2875,19 +2876,20 @@ bgp_evpn_skip_vrf_import_of_local_es(const struct prefix_evpn *evp,
 			return true;
 		}
 
-		/* Don't import routes with ES as destination if the nexthop
-		 * has not been advertised via the EAD-ES
+		/* Don't import routes with ES as destination if L3NHG is in
+		 * use and the nexthop has not been advertised via the EAD-ES
 		 */
 		if (pi->attr)
 			nh = pi->attr->nexthop;
 		else
 			nh.s_addr = INADDR_ANY;
-		if (install && !bgp_evpn_es_is_vtep_active(esi, nh)) {
+		if (install && !bgp_evpn_es_vrf_import_ok(bgp_vrf, esi, nh)) {
 			if (BGP_DEBUG(evpn_mh, EVPN_MH_RT)) {
 				char esi_buf[ESI_STR_LEN];
 
 				zlog_debug(
-					"vrf %s of evpn prefix %pFX skipped, nh %pI4 inactive in es %s",
+					"vrf %s %s of evpn prefix %pFX skipped, nh %pI4 inactive in es %s",
+					bgp_vrf->name,
 					install ? "import" : "unimport", evp,
 					&nh,
 					esi_to_str(esi, esi_buf,
@@ -2959,7 +2961,7 @@ static int install_uninstall_routes_for_vrf(struct bgp *bgp_vrf, int install)
 				/* don't import hosts that are locally attached
 				 */
 				if (bgp_evpn_skip_vrf_import_of_local_es(
-					    evp, pi, install))
+					    bgp_vrf, evp, pi, install))
 					continue;
 
 				if (is_route_matching_for_vrf(bgp_vrf, pi)) {
@@ -3168,13 +3170,14 @@ static int install_uninstall_route_in_vrfs(struct bgp *bgp_def, afi_t afi,
 		 || is_evpn_prefix_ipaddr_v6(evp)))
 		return 0;
 
-	/* don't import hosts that are locally attached */
-	if (bgp_evpn_skip_vrf_import_of_local_es(evp, pi, install))
-		return 0;
-
 	for (ALL_LIST_ELEMENTS(vrfs, node, nnode, bgp_vrf)) {
 		int ret;
 
+		/* don't import hosts that are locally attached */
+		if (bgp_evpn_skip_vrf_import_of_local_es(bgp_vrf, evp, pi,
+							 install))
+			continue;
+
 		if (install)
 			ret = install_evpn_route_entry_in_vrf(bgp_vrf, evp, pi);
 		else

bgpd/bgp_evpn_mh.c

@@ -1489,6 +1489,15 @@ void bgp_evpn_path_es_link(struct bgp_path_info *pi, vni_t vni, esi_t *esi)
 	listnode_add(es->macip_path_list, &es_info->es_listnode);
 }
 
+/* XXX - When a remote ES is added to a VRF, routes using that as
+ * a destination need to be migrated to a L2NHG and viceversa
+ */
+static void
+bgp_evpn_es_path_update_on_es_vrf_chg(struct bgp_evpn_es_vrf *es_vrf,
+				      bool active)
+{
+}
+
 static void
 bgp_evpn_es_path_update_on_vtep_chg(struct bgp_evpn_es_vtep *es_vtep,
 				    bool active)
@@ -1499,6 +1508,9 @@ bgp_evpn_es_path_update_on_vtep_chg(struct bgp_evpn_es_vtep *es_vtep,
 	struct bgp_path_info *parent_pi;
 	struct bgp_evpn_es *es = es_vtep->es;
 
+	if (!bgp_mh_info->host_routes_use_l3nhg)
+		return;
+
 	if (BGP_DEBUG(evpn_mh, EVPN_MH_RT))
 		zlog_debug("update paths linked to es %s on vtep chg",
 			   es->esi_str);
@@ -1714,7 +1726,7 @@ static void bgp_evpn_mac_update_on_es_oper_chg(struct bgp_evpn_es *es)
 			continue;
 
 		if (BGP_DEBUG(evpn_mh, EVPN_MH_RT))
-			zlog_debug("update path %s linked to es %s on vtep chg",
+			zlog_debug("update path %s linked to es %s on oper chg",
 				   prefix2str(&pi->net->p, prefix_buf,
 					      sizeof(prefix_buf)),
 				   es->esi_str);
@@ -2546,6 +2558,11 @@ static struct bgp_evpn_es_vrf *bgp_evpn_es_vrf_create(struct bgp_evpn_es *es,
 			   bgp_vrf->vrf_id, es_vrf->nhg_id, es_vrf->v6_nhg_id);
 	bgp_evpn_l3nhg_activate(es_vrf, false /* update */);
 
+	/* update paths in the VRF that may already be associated with
+	 * this destination ES
+	 */
+	bgp_evpn_es_path_update_on_es_vrf_chg(es_vrf, true);
+
 	return es_vrf;
 }
 
@@ -2559,6 +2576,11 @@ static void bgp_evpn_es_vrf_delete(struct bgp_evpn_es_vrf *es_vrf)
 		zlog_debug("es %s vrf %u nhg %u delete", es->esi_str,
 			   bgp_vrf->vrf_id, es_vrf->nhg_id);
 
+	/* update paths in the VRF that may already be associated with
+	 * this destination ES
+	 */
+	bgp_evpn_es_path_update_on_es_vrf_chg(es_vrf, false);
+
 	/* Remove the NHG resources */
 	bgp_evpn_l3nhg_deactivate(es_vrf);
 	if (es_vrf->nhg_id)
@@ -2656,24 +2678,54 @@ void bgp_evpn_es_evi_vrf_ref(struct bgpevpn *vpn)
 		bgp_evpn_es_vrf_ref(es_evi, vpn->bgp_vrf);
 }
 
+static bool bgp_evpn_es_vrf_use_nhg(struct bgp *bgp_vrf, esi_t *esi,
+				    struct bgp_evpn_es **es_p,
+				    struct bgp_evpn_es_vrf **es_vrf_p)
+{
+	struct bgp_evpn_es *es;
+	struct bgp_evpn_es_vrf *es_vrf;
+
+	if (!bgp_mh_info->host_routes_use_l3nhg)
+		return false;
+
+	es = bgp_evpn_es_find(esi);
+	if (!es)
+		return false;
+	if (es_p)
+		*es_p = es;
+
+	es_vrf = bgp_evpn_es_vrf_find(es, bgp_vrf);
+	if (!es_vrf)
+		return false;
+	if (es_vrf_p)
+		*es_vrf_p = es_vrf;
+
+	return true;
+}
+
+bool bgp_evpn_es_vrf_import_ok(struct bgp *bgp_vrf, esi_t *esi,
+			       struct in_addr nh)
+{
+	if (!bgp_evpn_es_vrf_use_nhg(bgp_vrf, esi, NULL, NULL))
+		return true;
+
+	return bgp_evpn_es_is_vtep_active(esi, nh);
+}
+
 /* returns false if legacy-exploded mp needs to be used for route install */
 bool bgp_evpn_path_es_use_nhg(struct bgp *bgp_vrf, struct bgp_path_info *pi,
 			      uint32_t *nhg_p)
 {
 	esi_t *esi;
-	struct bgp_evpn_es *es;
-	struct bgp_evpn_es_vrf *es_vrf;
+	struct bgp_evpn_es *es = NULL;
+	struct bgp_evpn_es_vrf *es_vrf = NULL;
 	struct bgp_path_info *parent_pi;
 	struct bgp_node *rn;
 	struct prefix_evpn *evp;
 	struct bgp_path_info *mpinfo;
 
 	*nhg_p = 0;
 
-	/* L3NHG support is disabled, use legacy-exploded multipath */
-	if (!bgp_mh_info->host_routes_use_l3nhg)
-		return false;
-
 	parent_pi = get_route_parent_evpn(pi);
 	if (!parent_pi)
 		return false;
@@ -2691,15 +2743,14 @@ bool bgp_evpn_path_es_use_nhg(struct bgp *bgp_vrf, struct bgp_path_info *pi,
 	if (!memcmp(esi, zero_esi, sizeof(*esi)))
 		return false;
 
-	/* if the ES-VRF is not setup or if the NHG has not been installed
-	 * we cannot install the route yet, return a 0-NHG to indicate
-	 * that
+	/* L3NHG support is disabled, use legacy-exploded multipath */
+	if (!bgp_evpn_es_vrf_use_nhg(bgp_vrf, esi, &es, &es_vrf))
+		return false;
+
+	/* if the NHG has not been installed we cannot install the route yet,
+	 * return a 0-NHG to indicate that
 	 */
-	es = bgp_evpn_es_find(esi);
-	if (!es)
-		return true;
-	es_vrf = bgp_evpn_es_vrf_find(es, bgp_vrf);
-	if (!es_vrf || !(es_vrf->flags & BGP_EVPNES_VRF_NHG_ACTIVE))
+	if (!(es_vrf->flags & BGP_EVPNES_VRF_NHG_ACTIVE))
 		return true;
 
 	/* this needs to be set the v6NHG if v6route */
@@ -2710,7 +2761,7 @@ bool bgp_evpn_path_es_use_nhg(struct bgp *bgp_vrf, struct bgp_path_info *pi,
 
 	for (mpinfo = bgp_path_info_mpath_next(pi); mpinfo;
 	     mpinfo = bgp_path_info_mpath_next(mpinfo)) {
-		/* if any of the paths of have a different ESI we can't use
+		/* if any of the paths have a different ESI we can't use
 		 * the NHG associated with the ES. fallback to legacy-exploded
 		 * multipath
 		 */

bgpd/bgp_evpn_mh.h

@@ -389,5 +389,7 @@ extern void bgp_evpn_es_vrf_show(struct vty *vty, bool uj,
 extern void bgp_evpn_es_vrf_show_esi(struct vty *vty, esi_t *esi, bool uj);
 extern void bgp_evpn_switch_ead_evi_rx(void);
 extern bool bgp_evpn_es_add_l3_ecomm_ok(esi_t *esi);
+extern bool bgp_evpn_es_vrf_import_ok(struct bgp *bgp_vrf, esi_t *esi,
+				      struct in_addr nh);
 
 #endif /* _FRR_BGP_EVPN_MH_H */