ICND2 Question - No IP Subnet-Zero

Node Man

Hi Everybody,
No Zero Subnet seems easy but has some tricky aspects. As in i get thrown off by trick questions easily. Im sorry to ask this way, but can someone spell out how No IP Subnet-zero really works?

Thanks

NetworkVeteran

IP Addressing: IPv4 Addressing Configuration Guide, Cisco IOS Release 12.4T - Configuring IPv4 Addresses  [Support] - Cisco Systems

IP Addressing: IPv4 Addressing Configuration Guide, Cisco IOS Release 12.4T - Configuring IPv4 Addresses  [Support] - Cisco Systems

Although, don't give their warnings too much weight, as this has been allowed for a very long time.