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Talk about MAC addresses, and IP addresses are never far behind. IP addresses operate in the TCP/IP reference model's network layer, responsible for forwarding data packets between networks. While IP addresses focus on network layer communication, MAC addresses operate at the data link layer, ensuring data frames are transmitted between nodes on the same network. Determining the location of a computer within a network is typically done using domain name addresses, IP addresses, or MAC addresses, each corresponding to different layers in the OSI model: application layer, network layer, and data link layer, respectively. Unlike IP addresses, which are dynamic, MAC addresses are fixed and uniquely assigned to a computer's network interface, much like a person's identification number.
MAC（Media Access Control，介质访问控制）地址也称为硬件地址，长度为48比特（6字节），由16进制数字组成，分为前24位和后24位。前24位称为组织唯一标志符（Organizationally Unique Identifier，OUI），是由IEEE的注册管理机构为不同厂家分配的唯一代码，用于区分不同的厂家。后24位由厂家自行分配，称为扩展标识符。同一厂家生产的网卡，其MAC地址的后24位通常会不同。MAC地址对应于OSI参考模型的数据链路层，交换机通过MAC地址维护节点和端口的数据库，在收到数据帧时根据目的MAC地址字段进行转发。
In a typical network communication process, IP addresses and MAC addresses work together to ensure data packets are layer-by-layer transmitted from client to server. For a better understanding, consider a client accessing a server. The data packet is transmitted through a series of nodes, such as A→B→C→F→G or A→B→E→F→G, as shown in the diagram. When a client accesses a server, it first resolves the domain name to an IP address, then sends data packets containing both the client's IP address and the server's IP address, along with the client's MAC address and the target MAC address. This process continues until the data packet reaches the destination server. Each network device, such as routers and switches, uses MAC addresses to forward data frames, ensuring seamless communication across the network.
When the server receives a request, it processes the request and sends a response data packet back to the client. For example, if the server sends a data packet labeled A to the client, the client acknowledges receipt and then waits for the next data packet, labeled B, or resends acknowledgment for packet A. This process ensures reliable communication between client and server.
客户端请求服务器的过程可以分为以下几个阶段：
在上述步骤2和4中，如果通信失败，系统会自动重试，直到数据包成功传输到目标节点并接收到成功响应。
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