Chapter 3. Integrated IS-IS Routing Protocol Concepts


A span of interconnected routers operated and managed by the same administrative group is referred to as an autonomous system of routers or a routing domain. Such a system of routers allows forwarding of data traffic from one location to the other. The current IS-IS specification, ISO 10589, refers to network nodes as intermediate systems, but this book uses the equivalent terminology of routers more frequently because it is more popular in current networking literature.

Individual routing domains are interconnected to form larger networks, such as the Internet, allowing transfer of data from one routing domain to the other over a large geographic span. Routers use routing protocols to learn about various locations within local or remote network domains. The two basic types of routing protocols follow:

  • Interior Gateway Protocols (IGPs) ” Optimized only for operation within a single network domain. IGPs are also known as intradomain routing protocols.

  • Exterior Gateway Protocols (EGPs) ” Optimized for exchange of routing information between domains. EGPs are also referred to as interdomain routing protocols.

IS-IS is designed and optimized to provide IGP functionality. The Border Gateway Protocol (BGP) is a well-known routing protocol with extensive capabilities for interdomain routing.

Typically, routing protocols support only one network layer protocol (Layer 3 in the OSI reference model). Therefore, when you use routers to provide connectivity for multiple Layer 3 protocols concurrently, they are usually configured with different routing protocols for each type of Layer 3 protocol supported. This approach is referred to as ships in the night.

As mentioned in the preceding chapter, Integrated IS-IS supports two network layer protocols: ISO CLNP and IP. Another routing protocol, which supports multiple Layer 3 protocols, is the Cisco proprietary Enhanced Interior Gateway Routing Protocol (EIGRP). EIGRP can be used to route IP, the Internet Packet Exchange Protocol (IPX), and AppleTalk all at the same time. Popular routing protocols that support only one network layer protocol include the NetWare Link Services Protocol (NLSP), which is based on the IS-IS protocol and supports only IPX; the Open Shortest Path First (OSPF) Protocol supports only IP. Versions 1 and 2 of the Routing Information Protocol (RIP) are also IP-only routing protocols. IS-IS and OSPF are similar in many regards and are the two most popular IGPs that are widely deployed in Internet service provider, IP-based enterprise networks.



IS-IS Network Design Solutions
IS-IS Network Design Solutions (Networking Technology)
ISBN: 1578702208
EAN: 2147483647
Year: 2005
Pages: 144
Authors: Abe Martey

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net