Lets take an interesting question on STP port priority.
why can we only change STP port-priority with an increments of 16 ?
Earlier when 802.1t standard was not into existance port priority and port ID was considered to be 8bits each, therefore ports ID in a switch can be in range 0 -255 and port priority in the range 0 -255 with increment of 1.
When 802.1t standard was defined, it describes port priority of 4bits and port ID of 12bits,therefore ports in a switch can be upto 4096 while port priority range is still 1-256 to provide backward compatibility with the older format. However now port priority has only 4 bits and to achieve port priority range 1-256, this had to make an increment of 16 so min value of port priority now is 0 and max value is 240 (16 values) with an increament of 16.
Here is the link to know more
