Posted on Thursday, 18th March 2004 by sean
IS-IS, or Intermediate System to Intermediate System is a new addition to the CCNP path. It is therefore likely that most people looking at the recertification will not have dealt with it.
The objectives associated with IS-IS are:
- Explain basic OSI terminology and network layer protocols used in OSI
- Identify similarities and differences between Integrated IS-IS and OSPF
- List the types of IS-IS routers and their role in IS-IS area design
- Describe the hierarchical structure of IS-IS areas
- Describe the concept of establishing adjacencies
- Given an addressing scheme and other laboratory parameters, identify the steps to configure Cisco routers for proper Integrated IS-IS operation
- Identify verification methods which ensure proper operation of Integrated IS-IS on Cisco routers
Cisco Press has a BCSN supplement for IS-IS that goes over the topic fairly well. In addition, Cisco has the IS-IS protocol family homepage on their site, especially look at the IS-IS Overview
Unfortunately, before we can get into the configuration of IS-IS, some background information is required.
Like OSPF, IS-IS is a link-state protocol meaning routers exchange information on links and calculate their own topology and best paths. Updates are also triggered on a change in the link state. IS-IS has its roots in the OSI protocols (not to be confused with the OSI stack model itself). It was originally meant to route CLNS/CLNP (more later), and was modified to also carry IP as a transitional measure until the OSI protocols took over the world. Hee hee.
As an OSI protocol, IS-IS uses OSI addresses, OSI PDUs, and OSI concepts, even if it is routing only IP.
The documents above are quite large, so it’s going to take me some time to get through them and into the next articles on IS-IS.
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