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
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.