Question 12 - JN0-280 discussion

An aggregate route is a summarized route that is created by combining multiple specific routes into a single, broader route. In Junos OS, when an aggregate route is configured, its default next hop is set to reject.

Step-by-Step Explanation:

Aggregate Route:

Aggregate routes are used to reduce the size of routing tables by representing a collection of more specific routes with a single summary route. They help improve routing efficiency and scalability, especially in large networks.

Default Next Hop Behavior:

When you configure an aggregate route in Junos OS, it has a reject next hop by default.

The reject next hop means that if a packet matches the aggregate route but there is no more specific route in the routing table for that destination, the packet will be discarded, and an ICMP 'destination unreachable' message is sent to the source.

This behavior helps to prevent routing loops and ensures that traffic isn't forwarded to destinations for which there is no valid route.

Modifying Next Hop:

If needed, the next hop behavior of an aggregate route can be changed to discard (which silently drops the packet) or to another specific next hop. However, by default, the next hop is set to reject.

Juniper

Reference:

Junos Command: set routing-options aggregate route <route> reject to configure an aggregate route with a reject next hop.

Verification: Use show route to verify the presence and behavior of aggregate routes.