3. Flow Specifications

3. Flow Specifications

A Flow Specification is an n-tuple consisting of several matching criteria that can be applied to IP traffic. A given IP packet is said to match the defined Flow Specification if it matches all the specified criteria. This n-tuple is encoded into a BGP NLRI defined below.

A given Flow Specification may be associated with a set of attributes, depending on the particular application; such attributes may or may not include reachability information (i.e., NEXT_HOP). Well-known or AS-specific community attributes can be used to encode a set of predetermined actions.

A particular application is identified by a specific (Address Family Identifier, Subsequent Address Family Identifier (AFI, SAFI)) pair [RFC4760] and corresponds to a distinct set of RIBs. Those RIBs should be treated independently from each other in order to assure noninterference between distinct applications.

BGP itself treats the NLRI as a key to an entry in its databases. Entries that are placed in the Loc-RIB are then associated with a given set of semantics, which is application dependent. This is consistent with existing BGP applications. For instance, IP unicast routing (AFI=1, SAFI=1) and IP multicast reverse-path information (AFI=1, SAFI=2) are handled by BGP without any particular semantics being associated with them until installed in the Loc-RIB.

Standard BGP policy mechanisms, such as UPDATE filtering by NLRI prefix as well as community matching, must apply to the Flow specification defined NLRI-type. Network operators can also control propagation of such routing updates by enabling or disabling the exchange of a particular (AFI, SAFI) pair on a given BGP peering session.