Header field identifiers can be dynamically bound to header fields in software defined networks via signaling between software defined network (SDN) controllers and switches. Dynamically establishing header binding definitions may allow new header fields to be recognized and manipulated (e.g., matched, modified, etc.) by SDN switches without having to update the corresponding standard. To achieve this, an SDN controller sends a binding request to an SDN switch to propose that a header field identifier be dynamically associated with a header field type. If the SDN switch acknowledges the binding request, then the header field identifier is used to identify the header field type in messages (e.g., control messages, etc.) transmitted to the SDN switch.