Orhan Ergun No Comments

IS-IS level 1, IS-IS Routing Protocol Levels

What is IS-IS Level 1 ? Why IS-IS level 1 is used ? What are the IS-IS levels ? What is the corresponding Area type in OSPF ?

IS-IS Level 1 is also called as IS-IS Level 1 sub domain. IS-IS is a link state routing protocol, similar to OSPF. You can read detail comparison of OSPF vs. IS-IS from here.

There is an Area concept in IS-IS as well but the purpose of IS-IS Areas are different than OSPF Areas.

In IS-IS Areas are used to create  IS-IS Levels and IS-IS Levels are the similar logical concepts with OSPF Areas.

 

Two create IS-IS Level 1 adjacency between two routers, same IS-IS area number should be used. Otherwise only IS-IS Level 2 adjacency can be created. This is the first rule of IS-IS adjacency relationship.

 

Which OSPF Area type is similar to IS-IS Level 1 Sub domain ?

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Orhan Ergun No Comments

IS-IS Suboptimal Routing Design

If you design multi level IS-IS network and if you have more than one exit (L1-L2 routers) from the Level 1 domain, you will likely create a suboptimal routing. Multi-level IS-IS design is for large-scale network. What’s more, most of the real life networks use only flat Level 2 IS-IS as their interior gateway protocol (IGP).

 

is-is routing protocol

 

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