zebra: Allow longer prefix matches for nexthops

Zebra currently does a shortest prefix match for
resolving nexthops for a prefix.  This is typically
an ok thing to do but fails in several specific scenarios.
If a nexthop matches to a route that is not usable, nexthop
resolution just gives up and refuses to use that particular
route.  For example if zebra currently has a covering prefix
say a 10.0.0.0/8.  And about the same time it receives a
10.1.0.0/16 ( a more specific than the /8 ) and another
route A, who's nexthop is 10.1.1.1.  Imagine the 10.1.0.0/16
is processed enough to know we want to install it and the
prefix is sent to the dataplane for installation( it is queued )
and then route A is processed, nexthop resolution will fail
and the route A will be left in limbo as uninstallable.

Let's modify the nexthop resolution code in zebra such that
if a nexthop's most specific match is unusable, continue looking
up the table till we get to the 0.0.0.0/0 route( if it's even
installed ).  If we find a usable route for the nexthop accept
it and use it.

The bgp_default_originate topology test is frequently failing
with this exact problem:

B>* 0.0.0.0/0 [200/0] via 192.168.1.1, r2-r1-eth0, weight 1, 00:00:21
B   1.0.1.17/32 [200/0] via 192.168.0.1 inactive, weight 1, 00:00:21
B>* 1.0.2.17/32 [200/0] via 192.168.1.1, r2-r1-eth0, weight 1, 00:00:21
C>* 1.0.3.17/32 is directly connected, lo, 00:02:00
B>* 1.0.5.17/32 [20/0] via 192.168.2.2, r2-r3-eth1, weight 1, 00:00:32
B>* 192.168.0.0/24 [200/0] via 192.168.1.1, r2-r1-eth0, weight 1, 00:00:21
B   192.168.1.0/24 [200/0] via 192.168.1.1 inactive, weight 1, 00:00:21
C>* 192.168.1.0/24 is directly connected, r2-r1-eth0, 00:02:00
C>* 192.168.2.0/24 is directly connected, r2-r3-eth1, 00:02:00
B>* 192.168.3.0/24 [20/0] via 192.168.2.2, r2-r3-eth1, weight 1, 00:00:32
B   198.51.1.1/32 [200/0] via 192.168.0.1 inactive, weight 1, 00:00:21
B>* 198.51.1.2/32 [20/0] via 192.168.2.2, r2-r3-eth1, weight 1, 00:00:32

Notice that the 1.0.1.17/32 route is inactive but the nexthop
192.168.0.1 is covered by both the 192.168.0.0/24 prefix( shortest match )
*and* the 0.0.0.0/0 route ( longest match ).  When looking at the logs
the 1.0.1.17/32 route was not being installed because the matching
route was not in a usable state, which is because the 192.168.0.0/24
route was in the process of being installed.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>

1 files changed, 36 insertions, 46 deletions

diff --git a/zebra/zebra_nhg.c b/zebra/zebra_nhg.c
index 6517b7830..19e2657f1 100644
--- a/zebra/zebra_nhg.c
+++ b/zebra/zebra_nhg.c
@@ -2248,20 +2248,6 @@ static int nexthop_active(struct nexthop *nexthop, struct nhg_hash_entry *nhe,
 		return 1;
 	}
 
-	if (top &&
-	    ((top->family == AF_INET && top->prefixlen == IPV4_MAX_BITLEN &&
-	      nexthop->gate.ipv4.s_addr == top->u.prefix4.s_addr) ||
-	     (top->family == AF_INET6 && top->prefixlen == IPV6_MAX_BITLEN &&
-	      memcmp(&nexthop->gate.ipv6, &top->u.prefix6, IPV6_MAX_BYTELEN) ==
-		      0)) &&
-	    nexthop->vrf_id == vrf_id) {
-		if (IS_ZEBRA_DEBUG_RIB_DETAILED)
-			zlog_debug(
-				"        :%s: Attempting to install a max prefixlength route through itself",
-				__func__);
-		return 0;
-	}
-
 	/* Validation for ipv4 mapped ipv6 nexthop. */
 	if (IS_MAPPED_IPV6(&nexthop->gate.ipv6)) {
 		afi = AFI_IP;
@@ -2364,7 +2350,7 @@ static int nexthop_active(struct nexthop *nexthop, struct nhg_hash_entry *nhe,
 					zlog_debug(
 						"        %s: Matched against ourself and prefix length is not max bit length",
 						__func__);
-				return 0;
+				goto continue_up_tree;
 			}
 
 		/* Pick up selected route. */
@@ -2391,20 +2377,12 @@ static int nexthop_active(struct nexthop *nexthop, struct nhg_hash_entry *nhe,
 		/* If there is no selected route or matched route is EGP, go up
 		 * tree.
 		 */
-		if (!match) {
-			do {
-				rn = rn->parent;
-			} while (rn && rn->info == NULL);
-			if (rn)
-				route_lock_node(rn);
-			continue;
-		}
 
 		/* If the candidate match's type is considered "connected",
 		 * we consider it first.
 		 */
-		if (RIB_CONNECTED_ROUTE(match) ||
-		    (RIB_SYSTEM_ROUTE(match) && RSYSTEM_ROUTE(type))) {
+		if (match && (RIB_CONNECTED_ROUTE(match) ||
+			      (RIB_SYSTEM_ROUTE(match) && RSYSTEM_ROUTE(type)))) {
 			match = zebra_nhg_connected_ifindex(rn, match,
 							    nexthop->ifindex);
 
@@ -2420,11 +2398,7 @@ static int nexthop_active(struct nexthop *nexthop, struct nhg_hash_entry *nhe,
 					zlog_debug(
 						"%s: %pNHv given ifindex does not match nexthops ifindex found: %pNHv",
 						__func__, nexthop, newhop);
-				/*
-				 * NEXTHOP_TYPE_*_IFINDEX but ifindex
-				 * doesn't match what we found.
-				 */
-				return 0;
+				goto continue_up_tree;
 			}
 
 			/* NHRP special case: need to indicate onlink */
@@ -2437,7 +2411,7 @@ static int nexthop_active(struct nexthop *nexthop, struct nhg_hash_entry *nhe,
 					__func__, match, match->nhe, newhop);
 
 			return 1;
-		} else if (CHECK_FLAG(flags, ZEBRA_FLAG_ALLOW_RECURSION)) {
+		} else if (match && CHECK_FLAG(flags, ZEBRA_FLAG_ALLOW_RECURSION)) {
 			struct nexthop_group *nhg;
 			struct nexthop *resolver;
 			struct backup_nh_map_s map = {};
@@ -2473,6 +2447,10 @@ static int nexthop_active(struct nexthop *nexthop, struct nhg_hash_entry *nhe,
 						"%s: match %p (%pNG) not installed or being Route Replaced",
 						__func__, match, match->nhe);
 
+				if (CHECK_FLAG(match->status,
+					       ROUTE_ENTRY_QUEUED))
+					goto continue_up_tree;
+
 				goto done_with_match;
 			}
 
@@ -2541,25 +2519,37 @@ done_with_match:
 				if (pmtu)
 					*pmtu = match->mtu;
 
-			} else if (IS_ZEBRA_DEBUG_RIB_DETAILED)
-				zlog_debug(
-					"        %s: Recursion failed to find",
-					__func__);
-
-			return resolved;
-		} else {
-			if (IS_ZEBRA_DEBUG_RIB_DETAILED) {
-				zlog_debug(
-					"        %s: Route Type %s has not turned on recursion",
-					__func__, zebra_route_string(type));
-				if (type == ZEBRA_ROUTE_BGP
-				    && !CHECK_FLAG(flags, ZEBRA_FLAG_IBGP))
+			} else {
+				if (IS_ZEBRA_DEBUG_RIB_DETAILED)
 					zlog_debug(
-						"        EBGP: see \"disable-ebgp-connected-route-check\" or \"disable-connected-check\"");
+						"        %s: Recursion failed to find while looking at %pRN",
+						__func__, rn);
+				goto continue_up_tree;
 			}
-			return 0;
+
+			return 1;
+		} else if (IS_ZEBRA_DEBUG_RIB_DETAILED) {
+			zlog_debug(
+				"        %s: Route Type %s has not turned on recursion %pRN failed to match",
+				__func__, zebra_route_string(type), rn);
+			if (type == ZEBRA_ROUTE_BGP
+			    && !CHECK_FLAG(flags, ZEBRA_FLAG_IBGP))
+				zlog_debug(
+					"        EBGP: see \"disable-ebgp-connected-route-check\" or \"disable-connected-check\"");
 		}
+
+	continue_up_tree:
+		/*
+		 * If there is no selected route or matched route is EGP, go up
+		 * tree.
+		 */
+		do {
+			rn = rn->parent;
+		} while (rn && rn->info == NULL);
+		if (rn)
+			route_lock_node(rn);
 	}
+
 	if (IS_ZEBRA_DEBUG_RIB_DETAILED)
 		zlog_debug("        %s: Nexthop did not lookup in table",
 			   __func__);