NE80 attaches two S8016s as convergence switch. NE80 connects NE5000E and NE5000E connects C12000 router.
IBGP session is built between NE80 and NE5000E. EBGP session is built between NE5000E and C12000.
NE5000E advertises convergence route with 22-bit mask through aggregate command. S8016 attached users of some network segment cannot access external network.
1. Not all users are stopped, physical link can be ironed out. Check device log and there is no alarm of link interruption.
2. Display bgp rout on NE80 and there is route to external network and to attached users.
3. Ping users on NE80 and it can be pinged through. The route from NE80 to user is reachable.
4. Ping users on NE5000E and it cannot be pinged through.
5. Execute disp bgp rout on NE5000E and it is found that the next-hop of BGP route less than 22-bit mask points to NE80, but the next-hop of BGP route with 22-bit mask points to NULL0.
6. The route pointing to NULL0 with 22-bit mask is related with aggregate. Delete aggregate and the next-hop of the route on NE5000E points to NE80, not NULL0.
7. The reason is that aggregate is not correctly used.
Aggregate command of BGP will auto aim at convergence route and create NULL0 route. The function is similar to the way of
network+static convergence route. Because the mask length of convergence route in aggregate command and that of route learnt from BGP on NE80 are the same, NE5000E auto creates convergence NULL0 route and drop all returned packets.
1. Aggregate command will auto create a route pointing to NULL0 for convergence route. In order to realize convergence route, the mask length must less than that of detailed route. Created NULL0 route will not cover detailed route.
2. To suppress detailed route advertisement, add detail-suppressed.