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The form of FDDI interface where a device is connected to both FDDI token-passing rings, so that uninterrupted operation continues 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 devices such as routers and concentrators are dual-attached, whereas host computers are normally single-attached or dual-homed to a router or concentrator.
For example, a ring could be formed between a single router and two concentrators (all dual-attached) then all other components that need to be fault-tolerant (typically file servers) can be dual-homed to both concentrators.