Embodiments of the invention relate to upbound input/output expansion requests and response processing in a PCIE architecture. A first request to perform an operation on a host system is intitiated. The first request is formatted for the first protocol and includes data that is required in order to process the first request. A second request is created in response to the first request, the second request includes a header and is formatted according to the second protocol. The data required to process the first request in the header of the second request is stored, and the second request is sent to the host system.