bgpd: Implicit updates in BGP may require a withdrawal from zebra RIB

*  J Yu <jackiesyu@hotmail.com> noted a problem with bgpd of routes not
   having their nexthop updated correctly.

   Martin Winter <mwinter@opensourcerouting.org> pinned this down to the
   case where a BGP route is updated from one with a valid nexthop to an
   invalid next-hop, using a test tool. Once the problem occurs, the incorrect
   route may remain, even after further UPDATEs, so long as the nexthop in the
   zebra RIB does not match the BGP route's nexthop.

   Jacqueline Yu then pinned the issue down further to being due to bgpd
   sending the DELETE for the route to zebra with the new nexthop after a
   BGP UPDATE updates an existing route, but then is found to be invalid,
   and zebra not finding the route as it requires a match on all attributes.

* bgp_zebra.c: (bgp_zebra_withdraw) When deleting a prefix, we want it gone.
  Do not send additional matching attributes like the nexthop, which can
  only cause incorrect non-matches.
Acked-by: Donald Sharp <sharpd@cumulusnetworks.com>

bgpd/bgp_zebra.c

@@ -863,18 +863,14 @@ bgp_zebra_withdraw (struct prefix *p, struct bgp_info *info, safi_t safi)
   if (p->family == AF_INET)
     {
       struct zapi_ipv4 api;
-      struct in_addr *nexthop;
 
       api.vrf_id = VRF_DEFAULT;
       api.flags = flags;
-      nexthop = &info->attr->nexthop;
 
       api.type = ZEBRA_ROUTE_BGP;
       api.message = 0;
       api.safi = safi;
-      SET_FLAG (api.message, ZAPI_MESSAGE_NEXTHOP);
-      api.nexthop_num = 1;
-      api.nexthop = &nexthop;
+      api.nexthop_num = 0;
       api.ifindex_num = 0;
       SET_FLAG (api.message, ZAPI_MESSAGE_METRIC);
       api.metric = info->attr->med;
@@ -882,10 +878,9 @@ bgp_zebra_withdraw (struct prefix *p, struct bgp_info *info, safi_t safi)
       if (BGP_DEBUG(zebra, ZEBRA))
 	{
 	  char buf[2][INET_ADDRSTRLEN];
-	  zlog_debug("Zebra send: IPv4 route delete %s/%d nexthop %s metric %u",
+	  zlog_debug("Zebra send: IPv4 route delete %s/%d metric %u",
 		     inet_ntop(AF_INET, &p->u.prefix4, buf[0], sizeof(buf[0])),
 		     p->prefixlen,
-		     inet_ntop(AF_INET, nexthop, buf[1], sizeof(buf[1])),
 		     api.metric);
 	}
 
@@ -897,54 +892,23 @@ bgp_zebra_withdraw (struct prefix *p, struct bgp_info *info, safi_t safi)
   if (p->family == AF_INET6)
     {
       struct zapi_ipv6 api;
-      unsigned int ifindex;
-      struct in6_addr *nexthop;
-      
-      assert (info->attr->extra);
       
-      ifindex = 0;
-      nexthop = NULL;
-
-      /* Only global address nexthop exists. */
-      if (info->attr->extra->mp_nexthop_len == 16)
-	nexthop = &info->attr->extra->mp_nexthop_global;
-
-      /* If both global and link-local address present. */
-      if (info->attr->extra->mp_nexthop_len == 32)
-	{
-	  nexthop = &info->attr->extra->mp_nexthop_local;
-	  if (info->peer->nexthop.ifp)
-	    ifindex = info->peer->nexthop.ifp->ifindex;
-	}
-
-      if (nexthop == NULL)
-	return;
-
-      if (IN6_IS_ADDR_LINKLOCAL (nexthop) && ! ifindex)
-	if (info->peer->ifname)
-	  ifindex = ifname2ifindex (info->peer->ifname);
-
       api.vrf_id = VRF_DEFAULT;
       api.flags = flags;
       api.type = ZEBRA_ROUTE_BGP;
       api.message = 0;
       api.safi = safi;
-      SET_FLAG (api.message, ZAPI_MESSAGE_NEXTHOP);
-      api.nexthop_num = 1;
-      api.nexthop = &nexthop;
-      SET_FLAG (api.message, ZAPI_MESSAGE_IFINDEX);
-      api.ifindex_num = 1;
-      api.ifindex = &ifindex;
+      api.nexthop_num = 0;
+      api.ifindex_num = 0;
       SET_FLAG (api.message, ZAPI_MESSAGE_METRIC);
       api.metric = info->attr->med;
 
       if (BGP_DEBUG(zebra, ZEBRA))
 	{
 	  char buf[2][INET6_ADDRSTRLEN];
-	  zlog_debug("Zebra send: IPv6 route delete %s/%d nexthop %s metric %u",
+	  zlog_debug("Zebra send: IPv6 route delete %s/%d metric %u",
 		     inet_ntop(AF_INET6, &p->u.prefix6, buf[0], sizeof(buf[0])),
 		     p->prefixlen,
-		     inet_ntop(AF_INET6, nexthop, buf[1], sizeof(buf[1])),
 		     api.metric);
 	}