IS/IS vs OSPF

it_consultant

I am re-learning OSPF today, basically the only routing protocol I have ever used, and we reviewed IS/IS. IS/IS seems much more efficient than OSPF. Does anyone here use IS/IS?

networker050184

I've worked in environments with both (working on an ISIS roll out now actually). Efficiency isn't something I would say is a big difference between the two as far as performance or configuration. Not having to have an area 0 is pretty handy in poorly designed or thrown together networks. The simple integration of IPv6 (and any future protocols) is a big plus though.

it_consultant

Do you have a personal preference? Just based on technical considerations, why don't more people use IS/IS?

networker050184

I think the reason people use OSPF is the same reason most people use Cisco. It's been pushed on them for years and its what they know! Most curriculum for learning networking technology is based around Cisco courses which are always heavy on OSPF and light on ISIS.

As far as personal preference, I've always liked OSPF but probably just for the reasons above. Its what I learned on and its what I've mostly used. Most people, myself included, go with the if it ain't broke don't fix it method and OSPF works!

I don't have any issue with ISIS other than the non user friendly ISO addressing scheme. With IPv6 deployments I think it will begin to be more preferred again in the provider space, but I doubt it will ever be big in the enterprise space because the expertise just isn't there for it to be supported.

W Stewart

Not too sure about what IS-IS is capable of but OSPF has a good amount of features that may or may not be available in IS IS like load balancing and choosing a route based off of reliability of the link and the current load already on the link and the ability to summarize on large networks in between areas. Not sure if IS-IS can do all of that but at my job we use EIGRP because of the ability to summarize without the concept of areas and the backup route that makes convergence faster. Plus you can do unequal cost load balancing. The problem with that is we have to use all cisco routers. From my understanding OSPF is more popular among networks that don't only use cisco routers. Again not completely sure what all IS IS is capable of but if you need them I believe OSPF may have a few extra features available.

it_consultant

IS/IS is a link state routing protocol that uses the Dijkstra algorithm for shortest path first routing. OSPF is the most deployed iBGP routing protocol, I am just wondering why there is no love thrown IS/IS' way.

W Stewart

Yea I haven't really heard much about IS-IS in the cisco books I'm reading. It might have been mentioned on network+

it_consultant

There are two main differences that I can tell. As networker pointed out, you don't need to connect through area 0 to route between areas in IS/IS. OSPF was originally written with (the details are somewhere but I can't recite them from memory) IPv4 built into the protocol, whereas IS/IS was not. This means that OSPF had to go though a re-write in order to be compatible with IPv6 whereas IS/IS needed minor tweaks only.

I remember at least one network I worked on where, if we had used IS/IS instead of OSPF, if would have been much easier and more efficient within our autonomous system(s).