This is a case study which provides a detailed design steps for IGP protocol on hypothetical Internet Service Provider, called Ausnet.
IS-IS Design considerations on MPLS backbone
Using IS-IS with MPLS require some important design considerations. IS-IS as a scalable link state routing protocol has been used in the Service Provider networks for decades.
In fact, eight of the largest nine Service Providers use IS-IS routing protocol on their network as of today. Read more
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 ?
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 is a link state routing protocol. Commonly used in Service Provider networks.
Back in old days, IS-IS routing protocol software was more stable and robust compare to OSPF, thus many service provider choose IS-IS as their interior routing protocol.
I collected the questions which I received from my students and readers related with IS-IS routing protocol and my answers in this post. Read more