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The form of FDDI interface where a device is connected toboth FDDI token-passing rings, so that uninterrupted operationcontinues in the event of a failure of either of the rings.All connections to the main FDDI rings are dual-attached.Typically, a small number of critical infrastructure devicessuch as routers and concentrators are dual-attached,whereas host computers are normally single-attached ordual-homed to a router or concentrator.For example, a ring could be formed between a single routerand two concentrators (all dual-attached) then all othercomponents that need to be fault-tolerant (typically fileservers) can be dual-homed to both concentrators.