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Chapter 6: Routing Policy Configuration Guide
SSR User Reference Manual 6 - 7
to know about individual subnets which would increase the size of its routing table, the
peer is only informed about an aggregate-route which contains all the subnets.
Like export policies, aggregate-routes can have up to three components:
• Aggregate-Destination
• Aggregate-Source
• Route-Filter
Aggregate-Destination
This component specifies the aggregate/summarized route. It also specifies the
attributes associated with the aggregate route. The preference to be associated with an
aggregate route can be specified using this component.
Aggregate-Source
This component specifies the source of the routes contributing to an aggregate/
summarized route. It can also specify the preference to be associated with the
contributing routes from this source. This preference can be overridden by explicitly
specifying a preference with the route-filter.
The routes contributing to an aggregate can be identified by their associated attributes:
• Protocol type (RIP, OSPF, BGP, Static, Direct, Aggregate).
• Autonomous system from which the route was learned.
• AS path associated with a route. When BGP is configured, all routes are assigned an
AS path when they are added to the routing table. For interior routes, this AS path
specifies IGP as the origin and no ASs in the AS path (the current AS is added when
the route is exported). For BGP routes, the AS path is stored as learned from BGP.
• Tag associated with a route. Both OSPF and RIP version 2 currently support tags.
All other protocols have a tag of zero.
In some cases, a combination of the associated attributes can be specified to identify
the routes contributing to an aggregate.
Route-Filter
This component specifies the individual routes that are to be aggregated or
summarized. The preference to be associated with these routes can also be explicitly
specified using this component.
The contributing routes are ordered according to the aggregation preference that
applies to them. If there is more than one contributing route with the same aggregating
preference, the route's own preferences are used to order the routes. The preference of
the aggregate route will be that of contributing route with the lowest aggregate
preference.