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If you don't use "ip classless'' command then by default whatever the IP you configure will be counted as classfull.It means if you want to configre81.62.34.0/24 automatically it will configure81.62.34.0/8.Because class A starts with0 and ends with127.So, when you configure VLSM IP you need that command.In real world it is always better to use 'ip classless'.Because public ip you get from your provider are not classful.