BigIron RX Series Configuration Guide 35953-1002253-01Overview of Rapid Spanning Tree Protocol 13FIGURE 40 Simple RSTP topologyPorts on Switch 1All ports on Switch 1, the root bridge, are assigned Designated port roles.Ports on Switch 2Port2 on Switch 2 directly connects to the root bridge; therefore, Port2 is the Root port.Switch 2’s bridge priority value is superior to that of Switch 3 and Switch 4; therefore, the ports onSwitch 2 that connect to Switch 3 and Switch 4 are given the Designated port role.Furthermore, Port7 and Port8 on Switch 2 are physically connected. The RST BPDUs transmitted byPort7 are superior to those Port8 transmits. Therefore, Switch 2 is the Backup port and Port7 is theDesignated port.Ports on Switch 3Port2 on Switch 3 directly connects to the Designated port on the root bridge; therefore, it assumesthe Root port role.The root path cost of the RST BPDUs received on Port4/Switch 3 is inferior to the RST BPDUstransmitted by the port; therefore, Port4/Switch 3 becomes the Designated port.Similarly, Switch 3 has a bridge priority value inferior to Switch 2. Port3 on Switch 3 connects toPort 3 on Switch 2. This port will be given the Alternate port role, since a Root port is alreadyestablished on this bridge.Switch 1Bridge priority = 100Switch 2Bridge priority = 200Switch 3Bridge priority = 300 Switch 4Bridge priority = 400Port2 Port2Port2Port3Port3 Port3Port3Port4 Port4Port4Port7 Port8
