What are two differences between OSPF and IS-IS?

OSPF is a link-state routing protocol, and IS-IS is a distance-vector routing protocol.

OSPF uses a router ID to identify a router, and IS-IS uses a system ID.

OSPF elects a DR and a BDR, and IS-IS elects a DIS.

Unlike OSPF. IS-IS supports virtual links.

Unlike IS-IS routers, an OSPF router belongs to only one area in addition to the backbone area.