This document presents a Topology-Transparent Zone (TTZ) in an OSPF area. A TTZ comprises a group of routers and a number of links connecting these routers. Any router outside of the zone is not aware of the zone. A TTZ hides the internal topology of the TTZ from the outside. It does not directly advertise any internal information about the TTZ to a router outside of the TTZ. The information about the links and routers such as a link down inside the TTZ is not advertised to any router outside of the TTZ.