There are many reasons of OSPF to IS-IS migration, specifically for the Service Provider networks. Some of these reasons are shared later in the case study.
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 ?
Why are dynamic routing protocols used is usually asked by newbies in the networking field, especially after they have heard about routing protocols. Besides that, they often asked this question: What is the difference between static routing and the dynamic routing protocols?
And the common answer is that dynamic routing protocols are scalable.
In other words, there is no need to configure a manual entry for each destination as well as specifying the next hop IP address or interface with the dynamic routing protocols.
These are good reasons. But do we really have only such benefits? In very small networks, scalability is reasonable and correct. But for more sophisticated networks, there are other important reasons.
Before I explain the other reasons, let me clarify why static routing requires lots of manual configurations and why it is not scalable, compared to dynamic routing protocols.
Figure- 1 Why are dynamic routing protocols used?
IS-IS, a link state routing protocol, requires careful attention during network design in order to avoid traffic blackholing. In the topology below, IS-IS routing protocol is used.
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).
I implore all my readers to always remember this topic: IGP LDP synchronization. It is important to use IGP LDP synchronization to avoid blackholing, especially when MPLS networks fails to function effectively.
Understanding everything about routing design is no brainer, especially if you have the chart below on your wall.
The table below highlights the pros and cons of each routing protocol. Of course, you need to consider the design attributes shown in Figure A before embarking on routing design.
Should you like the comparison of the routing protocols illustrated in the table below or should you want to see similar comparison for other technologies, feel free to add your comment in the comment section.
Another boon for all my readers!
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Figure A: Comparison of Routing Protocols
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
You need route redistribution for many reasons.
In this post,the drivers for the route redistribution but more importantly the best practices for applying route redistribution will be explained in great detail. Read more