1. network addressing rules
A. The network address must be unique.
B. The network ID cannot start with a number 127. In Class A addresses, the number 127 is reserved for the internal return function.
C. The first byte of the network logo cannot be 255. The number 255 is used as the broadcast address.
D. the first byte of the network ID cannot be "0". "0" indicates that the address is a local host and cannot be transferred.
2. Host addressing rules
A. The host ID must be unique in the same network.
B. each bit of the host ID cannot be "1". If all the bits are "1", the address of the host is the broadcast address, not the host address.
C. each bit of the host ID cannot be "0". If each bit is "0", it means "only this network", and there is no host on this network.
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