OSPF and ISIS are both are Link State Routing Protocols using the Dijkstra SPF Algorithm are Interior Gateway Protocols (IGP) they distribute routing information between routers belonging to a single Autonomous System (AS).
Furthermore, below features are supported by both protocols –
- Classless Inter-Domain Routing (CIDR)
- Variable Subnet Length Masking (VLSM)
- IP unnumbered links
Below table enumerates the difference between OSPF and ISIS protocols –