A network interface controller includes a media access controller and a host adapter. The host adapter includes a transmit route connected to receive an in-band packet from a host and further connected to transmit the in-band packet to the media access controller. The network interface controller also includes a sideband port controller connected to receive a sideband packet destined for a network from a sideband endpoint and further connected to transmit the sideband packet to the host adapter. The host adapter further includes a host buffer to store the in-band packet, a sideband buffer to store the sideband packet, and an arbiter connected to allow, at different times, the in-band packet to advance along the transmit route from the host buffer to the media access controller and the sideband packet to advance along the transmit route from the sideband buffer to the media access controller.