Operation Manual – MSTPH3C S3100 Series Ethernet Switches Chapter 1 MSTP Configuration1-24Caution:z Once you specify a switch as the root bridge or a secondary root bridge by using thestp root primary or stp root secondary command, the bridge priority of the switchcannot be configured any more.z During the selection of the root bridge, if multiple switches have the same bridgepriority, the one with the smallest MAC address becomes the root bridge.II. Configuration example# Set the bridge priority of the current switch to 4,096 in spanning tree instance 1. system-view[Sysname] stp instance 1 priority 40961.3.5 Configuring the Mode a Port Recognizes and Sends MSTP PacketsA port can be configured to recognize and send MSTP packets in the following modes.z Automatic mode. Ports in this mode determine the format of the MSTP packets tobe sent according to the format of the received packets.z Legacy mode. Ports in this mode recognize/send packets in legacy format.z 802.1s mode. Ports in this mode recognize/send packets in dot1s format.A port acts as follows according to the format of MSTP packets forwarded by a peerswitch or router.When a port operates in the automatic mode:z The port automatically determines the format (legacy or dot1s) of received MSTPpackets and then determines the format of the packets to be sent accordingly, thuscommunicating with the peer devices.z If the format of the received packets changes repeatedly, MSTP will shut down thecorresponding port to prevent network storm. A port shut down in this way can onlybe brought up by the network administrator.When a port operates in the legacy mode:z The port only recognizes and sends MSTP packets in legacy format. In this case,the port can only communicate with the peer through packets in legacy format.z If packets in dot1s format are received, the port turns to discarding state to preventnetwork storm.When a port operates in the 802.1s mode:z The port only recognizes and sends MSTP packets in dot1s format. In this case,the port can only communicate with the peer through packets in dot1s format.
