During BGP configuration on a router that has peered with other BGP speakers, the BGP
command aggregate-address 172.32.0.0 255.255.252.0 is issued. However, the peers do not
receive this aggregate network in BGP advertisements. Also, the router does not have this
aggregate network in its BGP table. Which option indicates a possible reason this command did
not cause the router to advertise the aggregate network to its peers?
A.
Interface NULL 0 is likely shutdown.
B.
The BGP command no synchronization is missing.
C.
The BGP command no auto-summary is missing.
D.
Subnets of 172.32.0.0/22 do not exist in the BGP table.
E.
The IGP running on this router does not have network 172.32.0.0/22 installed.
F.
The next hop IP address must be a loopback address.
Explanation:
BGP allows the aggregation of specific routes into one route using the “aggregate-address
address mask” command. Aggregation applies to routes that exist in the BGP routing table. This is
in contrast to the network command, which applies to the routes that exists in IP routing table.
Aggregation can be performed if at least one or more of the specific routes of the aggregate
address exists in the BGP routing table.Reference:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800945ff.shtml