Atomic Aggregate and Aggregator Attributes

The Atomic Aggregate attribute informs BGP peers that the local router is using a less specific (aggregated) route to a destination.

If a BGP speaker selects a less specific route, when a more specific route is available, it must attach the Atomic Aggregate attribute when propagating the route. The Atomic Aggregate attribute lets the BGP peers know that the BGP speaker used an aggregated route.

When you use the Atomic Aggregate attribute, the BGP speaker has the option to send the Aggregator attribute. The Aggregator attribute includes the AS number and the IP address of the router that originated the aggregated route. In Cisco routers, the IP address is the RID of the router that performs the route aggregation. Atomic Aggregate is a well-known attribute and Aggregator is an optional, transitive attribute.

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