BGP-4 is capable of operating in an environment where a set of reachable destinations may be expressed via a single IP prefix. The concept of network classes, or subnetting is foreign to BGP-4. To accommodate these capabilities BGP-4 changes semantics and encoding associated with the AS_PATH attribute. New text has been added to define semantics associated with IP prefixes. These abilities allow BGP-4 to support the proposed supernetting scheme [9].
To simplify configuration this version introduces a new attribute, LOCAL_PREF, that facilitates route selection procedures. The INTER_AS_METRIC attribute has been renamed to be MULTI_EXIT_DISC. A new attribute, ATOMIC_AGGREGATE, has been introduced to insure that certain aggregates are not de-aggregated. Another new attribute, AGGREGATOR, can be added to aggregate routes in order to advertise which AS and which BGP speaker within that AS caused the aggregation.
To insure that Hold Timers are symmetric, the Hold Time is now negotiated on a per-connection basis. Hold Times of zero are now supported.