Specifies a protocol used by Network Layer entities in End Systems (ES) and Intermediate Systems (IS) to maintain routing information. Defines: transmission procedures for configuration and routing information between ES and IS, the encoding of protocol data units, procedures for protocol control information interpretation, functional requirements for implementations conforming with this standard. References: ISO 7498, 7498 Add. 1 and 4, 8208, 8348 Add. 1 and 2, ISO 8473, 8648, 8802, CCITT X.25.