Specifies a protocol to be used by boundary intermediate systems to acquire and maintain information for the purpose of routeing NPDUs between different routeing domains. Lays down the procedures for the exchange of inter-domain reachability and path information between BISs, the procedures for maintaining inter-domain routeing information bases within a BIS, the encoding of protocol data units used to distribute inter-domain routeing information between BISs, the functional requirements for implementations that claim conformance to this standard. The protocol described operates at the level of individual routeing domains. Does not cover the establishment of administrative domains.