Configuring Aggregate Routes

Route aggregation allows you to combine groups of routes with common addresses into a single entry in the routing table. This decreases the size of the routing table as well as the number of route advertisements sent by the router.

An aggregate route becomes active when it has one or more contributing routes. A contributing route is an active route that is a more specific match for the aggregate destination. For example, for the aggregate destination 128.100.0.0/16, routes to 128.100.192.0/19 and 128.100.67.0/24 are contributing routes, but routes to 128.0.0.0./8, 128.0.0.0/16, and 128.100.0.0/16 are not.

A route can contribute only to a single aggregate route. However, an active aggregate route can recursively contribute to a less specific matching aggregate route. For example, an aggregate route to the destination 128.100.0.0/16 can contribute to an aggregate route to 128.96.0.0/13.

When an aggregate route becomes active, it is installed in the routing table with the following information:

• Reject next hop—If a more-specific packet does not match a more-specific route, the packet is rejected and an ICMP unreachable message is sent to the packet’s originator.
• Metric value as configured with the aggregate statement.
• Preference value that results from the policy filter on the primary contributor, if a filter is specified.
• AS path as configured in the aggregate statement, if any. Otherwise, the path is computed by aggregating the paths of all contributing routes.
• Community as configured in the aggregate statement, if any is specified.

  Note: You can configure only one aggregate route for each destination prefix.

To configure aggregate routes in the default routing table (inet.0), include the aggregate statement:

To configure aggregate routes in one of the other routing tables, or to explicitly configure aggregate routes in the default routing table (inet.0), include the aggregate statement:

For a list of hierarchy levels at which you can include these statements, see the statement summary sections for these statements.

Note: You cannot configure aggregate routes for the IPv4 multicast routing table (inet.1) nor the IPv6 multicast routing table (inet6.1).

The aggregate statement consists of two parts:

• defaults—Here you specify global aggregate route options. These are treated as global defaults and apply to all the aggregate routes you configure in the aggregate statement. This part of the aggregate statement is optional.
• route—Here you configure individual aggregate routes. In this part of the aggregate statement, you optionally can configure aggregate route options. These options apply to the individual destination only and override any options you configured in the defaults part of the aggregate statement.

The following topics provide more information about configuring aggregate routes:

• Configuring the Destination of Aggregate Routes
• Configuring Aggregate Route Options
• Applying Policies to Aggregate Routes
• Advertising Aggregate Routes