HTTP通信中服务器对客户端IP、MAC地址的获取与存储技术问询

1. Does the server know the client's IP address to send an HTTP response? #

Absolutely yes—this is fundamental to how TCP/IP works, and HTTP relies entirely on TCP for transport.

When you send an HTTP request, the first step is a TCP three-way handshake between your client and the server. During this handshake, your client's IP address and source port are sent to the server, which stores this information (along with its own IP and port, forming a "TCP connection quadruplet").

Without this IP address, the server would have no idea where to route the response packets. Even at the HTTP layer, server software (like Nginx, Apache, or a custom Node.js app) can access this IP address—you've probably seen it in server logs, where every request is tagged with the client's IP.

2. If the client disconnects after sending an HTTP request and waits for a response, does the server store the client's IP and MAC address? Are these details stored when the TCP connection is established? #

Let's break this into clear parts:

• Disconnecting after sending the request: If your client sends the HTTP request and immediately closes the TCP connection (sends a FIN packet), the server's TCP stack will detect that the connection is closed. If the server hasn't already sent the response, it may attempt to send it anyway—but your client's closed socket will likely send a RST (reset) packet back, and the response won't reach you. In short, you can't disconnect and then wait for a response; the TCP connection needs to be active (or at least in a state where the server can send data) for the response to be delivered.
• Stored information: The server does store your client's IP address and source port (as part of the TCP connection quadruplet) while the connection is active. However, it does NOT store your MAC address. MAC addresses are a link-layer protocol—they only work within a single local network. If you're connecting to a server across the internet, your packets pass through routers, each of which replaces the source MAC address with its own. By the time the packet reaches the server, the MAC address it sees belongs to its own gateway router, not your client's network interface.
• When are details stored?: All the necessary TCP connection details (client IP, client port, server IP, server port) are stored by the server's operating system as soon as the TCP three-way handshake completes and the connection is established. The HTTP server can then retrieve this IP address from the OS when handling the request.

内容的提问来源于stack exchange，提问作者qubit01