IS-IS vs. OSPF Part I: First steps in understanding IS-IS
The theme question is actually quite a good one, because it may seem like the fight has already been won by IS-IS in the Service Provider segment, and by OSPF on the enterprise market. So why ask it then? Well, because I got the following answer one too many times: “IS-IS is awesome, OSPF not so much. I have no idea how IS-IS works but it’s great. OSPF is so complicated and offers so little flexibility…”.
Well, that’s really wrong from my point of view. No protocol can be neither awesome nor despicable. They both offer you advantages and disadvantages, and knowing how they both work will help you make the best decision based on the needs of the network, not just because people say one is “great” and the other is not.
So, I am going to follow the steps I took to come to terms with IS-IS, and then we’ll see together, even though you’ll probably figure it out for yourselves by then, the comparative analysis of the two IGPs.
Step 1: Understanding CLNS & CLNP
Often network engineers freak out when they hear about the OSI stack, CLNP (Connectionless Network Protocol) and CLNS (Connectionless Network Service). Continue reading