BSCI - IS-IS - Differences between IS-IS and OSPF

• OSPF supports 50 routers per area
• IS-IS can support up to 1000 routers per area
• OSPF includes more features, including route tags, stub/nssa configuration, on demand circuits
• OSPF requires many LSA's to advertise and withdraw routes.
• IS-IS only requires one LSP per IS-IS router in a given area.
• IS-IS doesn't support a Backup designated router (BDR).i.e. you only have the primary Designated Intermediate System (DIS).
• IS-IS repeats the DIS election process every time a new router is added to an area.
• If the new router has the same of higher priority it will become the new DIS.
• IS-IS is designed to be deterministic so that the same set of IS-IS routers always produce the same DIS.
• Every time a DIS changes a new set of LSP's are flooded to the neighbours.
• IS-IS form adjacencies with all routers in the area not just the DIS.
• OSPF uses a scaled metric by default where as IS-IS uses a default metric of 10 for all links.