Disclosed are a communication system. All nodes in the communication system belong to a same layer 2 network. Well-known information of the layer 2 network can be obtained by the node. The node obtains the well-known information and forms a well-known key based on the well-known information and a preset key derivation algorithm; obtains a local MAC address of a first node and forms a first random number; forms first plaintext data based on the local MAC address and the first random number; and encrypts the first plaintext data based on the well-known key and a symmetric encryption algorithm, to form a first network layer address. Each node forms the well-known key based on the well-known information and the key derivation algorithm, and forms the network layer address based on the well-known key, the local MAC address, and the symmetric encryption algorithm.