An input/output (I/O) device includes a host interface for connection to a host device having a memory, and a network interface, which is configured to transmit and receive, over a network, data packets associated with I/O operations directed to specified virtual addresses in the memory. Processing circuitry is configured to translate the virtual addresses into physical addresses using memory keys provided in conjunction with the I/O operations and to perform the I/O operations by accessing the physical addresses in the memory. At least one of the memory keys is an indirect memory key, which points to multiple direct memory keys, corresponding to multiple respective ranges of the virtual addresses, such that an I/O operation referencing the indirect memory key can cause the processing circuitry to access the memory in at least two of the multiple respective ranges.