Rapid Spanning Tree Protocol (RSTP) - How to change specific link to forwarding in Spanning Tree Protocol ?
Users change the port priority in order to specify the forwarding port and/or blocking port. In general, the port with smaller port priority ID would be configured as the forwarding port whereas the port with bigger port priority ID would be the blocking port. For example, if users want to configure SW1 port 27 as forwarding port and the port priority ID of SW4 port 26 is 128, the port priority ID of SW1 port 27 should be changed to a number smaller than 128.
SW_1(config)#interface ethernet 1/27
SW_1(config-if)#spanning-tree port-priority ?
<0-240> Spanning-tree port priority value in steps of 16
*Please note that the port priority value is steps of 16 in range of 0-240.
SW_4(config-if)#spanning-tree port-priority 16