Routing Architecture

1 Abstract Digital developed the intermediate system-to-intermediate system (IS-IS) intradomain routing information exchange protocol for the DECnet Phase V network layer architecture. This protocol, which has been adopted by the International Organization for Standardization, is based on a link state routing algorithm. The benefits derived from the IS-IS protocol include a self-stablizing method for reliable link state packet distribution, a hierarchical network structure to support larger networks, protocols for efficiently utilizing local area networks, and simultaneous support for multiple network layer protocols. The network layer architecture has three basic components. The first concerns the transmission of data packets from one end system (a host) to a remote end system, regardless of whether or not these packets are sent by way of routers. The main features of this component are packet formats and addressing. Standards for these features are defined in the connectionless network layer protocol (CLNP), adopted by the International Organization for Standardization (ISO), and in the internet protocol (IP), the equivalent standard in the transmission control protocol/internet protocol (TCP/IP) suite.[1,2] The second component relates to handshaking between neighbors (i.e., directly connected systems) and mapping network layer addresses to data link layer addresses. The ISO protocol that performs this function is the end system-to-intermediate system (ES-IS) protocol.[3] The address resolution and internet control message protocols provide most of the same functionality in the TCP/IP protocol suite.[4,5] The third component of the network layer architecture pertains to routing. The routing protocol developed for Digital's DECnet Phase V network architecture and adopted by the ISO is the intermediate system-to-intermediate system (IS-IS) intradomain routing information exchange protocol.[6] The architecture for DECnet Phase V allows support of many network layer protocols, i.e., CLNP, IP, Novell NetWare, and AppleTalk.[7] Each network layer suite has its own protocols for the first two components of the network layer architecture. DECnet Phase V support for a particular network layer suite implies support for such protocols. Consequently, end systems that implement an existing network layer protocol need not be modified to operate with DECnet Phase V routers (i.e., intermediate systems). This paper briefly discusses data packet formats, types of routing control packets, and neighbor handshaking protocols and then focuses on the third