The spelling of the word "IS-IS" can be confusing to those unfamiliar with its pronunciation. It is pronounced /ˈaɪz ˌaɪz/ and written with hyphens to denote that each letter is pronounced separately. The first "IS" is pronounced as the sound of the letter "i" followed by the sound of the letter "s". The second "IS" is pronounced with the same sounds but reversed. This word refers to the Intermediate System to Intermediate System protocol used in computer networking.
IS-IS, abbreviated for Intermediate System to Intermediate System, is a routing protocol used in computer networks to enable the exchange of information between routers. It is categorized as an Interior Gateway Protocol (IGP), designed for large, complex networks known as autonomous systems.
IS-IS employs a link-state algorithm that allows routers to construct an accurate, synchronized view of the network topology. This protocol uses the concept of "areas" to divide the network into smaller, more manageable units. Each area has its own link-state database, which stores information about the connected routers, links, and their respective metrics.
IS-IS utilizes a hierarchical structure, with levels defined for the routers within an autonomous system. Level 1 routers are responsible for intra-area routing, exchanging routing information with other routers within their own area. Level 2 routers handle inter-area routing, distributing routing information between areas. Level 1-2 routers are capable of performing both intra-area and inter-area routing.
IS-IS utilizes a robust and reliable update mechanism, using Link-State Protocol Data Units (LSPs) to share information across the network. LSPs contain details about the network topology, including available paths, network addresses, and metrics. Each router maintains its own LSP, periodically refreshing and sharing it with neighboring routers, allowing for rapid convergence, fault tolerance, and load balancing.
IS-IS is commonly used in large-scale enterprise networks, telecommunications networks, and internet service providers (ISPs). It is highly scalable, efficient, and supports different network technologies, including IPv4 and IPv6.
The word "IS-IS" stands for Intermediate System to Intermediate System. It is a routing protocol in computer networking. The etymology of the word comes from the system it was designed to replace, which is called the Interior Gateway Routing Protocol (IGRP). As IGRP was developed by Cisco Systems, they named its successor the Interior Gateway Exchange Protocol (IGRP-X). However, the name IGRP-X was believed to cause confusion and be mistaken as an extension to IGRP. To avoid this, the name IS-IS was chosen instead, reflecting its purpose of routing between intermediate systems.