Cisco CCNP / BSCI Certification: Introduction To ISIS Terminology

When you're studying to pass the BSCI exam and earn your CCNP certification, you're going to be introduced to ISIS. ISIS and OSPF are both link-state protocols, but ISIS works quite differently from OSPF. You must master these details in order to earn your CCNP.

One of the major differences between OSPF and ISIS will be evident to you when you first begin your BSCI exam studies, and that is the terminology. ISIS uses terms that no other protocol you've studied to date uses, and learning these new terms is the first step to BSCI and CCNP exam success.

First off, what does "IS" stand for in "ISIS"? It stands for "Intermediate System", which sounds like a group of routers. As opposed to Autonomous Systems, which are logical groups of routers, an Intermediate System is simply a single router. That's it.

You'll also become familiar with End Systems, referred to in ISIS as an "ES". The End System is simply an end host.

ISIS and OSPF both use the concept of areas, but ISIS takes a different approach to this concept. ISIS routers use three different types of routing levels, according to the area a router has been placed in. Level 2 routers are connected only to the backbone and serve as a transit device between non-backbone areas. Level 1 routers are totally internal to a non-backbone area.

ISIS uses both Level-1 and Level-2 Hellos, meaning that the two types of routers just mentioned cannot form an adjacency. Luckily for us, there is a middle ground, and that is the Level 1-2 router. These routers connect non-backbone areas to backbone areas. L1-L2 routers keep two separate routing tables, one for L1 routing and another for L2 routing. This is the default setting for a Cisco router, and L1-L2 routers can form adjacencies with both L1 and L2 routers.

Part of the challenge of learning ISIS is getting used to the differences between ISIS and OSPF. Keep studying the terminology, master one concept at a time, and soon you'll be a master of ISIS and a CCNP to boot!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of over 100 free certification exam tutorials, including Cisco CCNA certification test prep articles. His exclusive Cisco CCNA study guide and Cisco CCNA training is also available!

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CCNA E-Books

CCNA is Cisco Certified Network Associate. It is an entry or "apprentice" level networking certification. Cisco created the CCNA to know basic ability in computer networking, particularly for installation and support of LAN/WAN networks having 100 nodes or fewer. The CCNA covers both IP and non-IP networks, including Novell IPX and AppleTalk. Obtaining the CCNA requires passing a single certification exam. Although the CCNA has no formal fundamentals, one must effectively complete hundreds of hours of study in preparation. Primarily, one must understand basic routing and switching as they relate to network design, performance and security. Additional background information on the CCNA with links to study notes and practice exams may be obtained.

E-books are electronic versions of printed books. CCNA E-books can be viewed on the Internet. Since E-books are online, they are available at your convenience, anywhere, anytime. E-books are "checked out" only for the period of time you are actively reading online and they are "returned" for the next user at the end of your use. Only one reader at a time can read a book online. Using E-books is easy. No passwords or user names are necessary. This document is written to the networking professional. It is not a brain-dump or a text book. If you find an E-book in the library catalog and want to read it, you can write down the title and find the E-book by using the access route through the "fulltext articles" selection. Validation is possible with your library card"s barcode number. E-books are identical to printed textbooks, but cost about half as much. Some E-book downloads require the use of Adobe Reader, while others use Zinio Reader.

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