IS PROTOCOL IS-IS REALY USED IN REAL WORLDþ

performance is fine (although that depends on scale, boxes used, manufacturer, tuning etc).

traditionally it was used most at ISPs and was always regarded as more scaleable, and since it doesnt use IP to carry its packets it is often regarded as a bit more secure - carriers are / were the main users.

You also find it in other kinds of network - a lot of SDH networks use IS-IS to route their control networks (since a lot of muxes operate on OSI CLNS).

it has different scaling properties to OSPF - you can get "bigger areas" in OSPF terms, and the hierarchy is slightly different in that any 1 router is in 1 area - no real concept of an ABR.

As with most routing protocols IS-IS has been improved over the years

- "wide" interface costs for example were retrofitted after comparisons with OSPF.