# Pastebin GoX53xQq

Use Case 3B: New Client communicating with a Old Ironic (user-specified)

This is the where the user requests a particular microversion to a new client that support microversions and tries to communicate with an old Ironic.

    The user specifies a microversion that is valid for the client.
    The client makes a connection to an old Ironic, supplying a X-OpenStack-Ironic-API-Version HTTP header
    Ironic doesn’t look for, or parse the HTTP header. It communicates using the only API code path it knows about, that being v1.0
    The client does not receive a X-OpenStack-Ironic-API-Version header in the response, and from that is able to assume that the version of Ironic that it is talking to does not support microversions. That is, it is using a version of the REST API that predates v1.0.
    The client informs the user that it cannot communicate to Ironic using that microversion and exits.