You want several different subnets within your enterprise network to be reachable from outside the enterprise network. Your edge router must share a single route advertisement about these subnets with external devices. If one of the subnets is unavailable, your edge router should drop any traffic destined to that subnet.

Which type of route, configured on the edge device with default behavior, accomplishes these objectives?

A.
an aggregate route

B.
a generated route

C.
a primary contributing route

D.
an OSPF route

Explanation:
Configuring Aggregate Route Options
In the defaults and route parts of the aggregate statement, you can specify aggregate-options, which define additional information about aggregate routes that is included with the route when it is installed in the routing table. All aggregate options are optional. Aggregate options that you specify in the defaults part of the aggregate statement are treated as global defaults and apply to all the aggregate routes you configure in the aggregate statement. Aggregate options that you specify in the route part of the aggregate statement override any global aggregate options and apply to that destination only.
To configure aggregate route options, include one or more of them in the defaults or route part of the aggregate statement:

[edit]
routing-options {
aggregate {
(defaults | route) {
(active | passive);
as-path <as-path> <origin (egp | igp | incomplete)> <atomic-aggregate> <aggregator as-number in-address>;
community [ community-ids ];
discard;
(brief | full);
(metric | metric2 | metric3 | metric4) metric <type type>;
(preference | preference2 | color | color2) preference <type type>;
tag string;
}
}
}