Specify a Next Hop for a Route

By default, when aggregate routes are installed in the routing table, the next hop is configured as a reject route. That is, the packet is rejected and an ICMP unreachable message is sent to the packet's originator.

When you configure an individual route in the route part of the aggregate statement, or when you configure the defaults for aggregate routes, you can specify a discard next hop. This means that if a more specific packet does not match a more specific route, the packet is rejected and a reject route for this destination is installed in the routing table, but ICMP unreachable messages are not sent. Being able to discard next hops allows you to originate a summary route, which is advertisable through dynamic routing protocols, and allows you to discard received traffic that does not match a more specific route than the summary route. To
discard next hops, include the discard option:

[edit routing-options aggregate defaults] 

discard;

For a list of hierarchy levels at which you can configure this statement, see the statement summary section for this statement.