A method, data processing system, and computer usable code are provided for protocol definition for software bridge failover. In a first aspect of the present invention, a first software bridge determines the proper working operation of a physical adapter. Limbo packets are sent to a second software bridge alerting the second software bridge that the first software bridge is no longer bridging traffic responsive to the physical adapter failure in the first software bridge. The second software bridge receives the limbo packets, and, in response to receiving the limbo packets, asserts primary control and initiates bridging of traffic. In an alternative aspect of the present invention a first software bridge sends keep-alive packets. A second software bridge monitors the keep-alive packets from the first software bridge and, in response to a failure to detect the keep-alive packets from the first software bridge, the second software bridge initiates bridging of traffic.