A conformant BGP-4 implementation is required to have the ability to specify when an aggregated route may be generated out of partial routing information. For example, a BGP speaker at the border of an autonomous system (or group of autonomous systems) must be able to generate an aggregated route for a whole set of destination IP addresses (in BGP-4 terminology such a set is called the Network Layer Reachability Information or NLRI) over which it has administrative control (including those addresses it has delegated), even when not all of them are reachable at the same time.
A conformant implementation may provide the capability to specify when an aggregated NLRI may be generated.
A conformant implementation is required to have the ability to specify how NLRI may be de-aggregated.
A conformant implementation is required to support the following options when dealing with overlapping routes:
Certain routing policies may depend on the NLRI (e.g. "research" versus "commercial"). Therefore, a BGP speaker that performs route aggregation should be cognizant, if possible, of potential implications on routing policies when aggregating NLRI.