This read-write enumerated integer configures which bridging mode a given port operates in: transparentonly(1), sourcerouteonly(2), or srt(3) for mixed source-route transparent bridging, determining whether the bridge converts between Source Routing and Transparent packet formats on that port. An administrator sets this per port to match the port's connected network segment type, since a mismatch prevents proper frame format conversion between Token Ring source-routed segments and transparent Ethernet segments. For example, on a port that bridges a legacy Token Ring source-routed segment to an Ethernet backbone, the admin sets this to srt(3) so the bridge performs the necessary source-route-to-transparent conversion.