TCP数据包目的端识别及多浏览器多标签80端口流量区分疑问

Alright, let's break down your questions one by one—these are such common, fundamental questions when you're getting into how TCP works, so glad you asked!

To figure out the destination of a TCP packet, you need to look at two key parts of the network stack:

• IP Header: This contains the destination IP address—it tells your network exactly which host (computer/server) the packet is meant for. Without this, the packet wouldn't know which machine to reach across the internet or local network.
• TCP Segment Header: Nestled inside the IP packet is the TCP segment, which has the destination port number. Once the packet reaches the target host, the operating system uses this port number to route the data to the correct application (like a web server listening on port 80).

Put together, the destination IP + destination port forms the core of identifying where the TCP data needs to end up. Think of the IP address as the street address of a building, and the port number as the apartment number inside that building.

This is where the TCP four-tuple comes in—it's the secret sauce that makes this all work. The four-tuple consists of:
源IP地址 + 源端口号 + 目的IP地址 + 目的端口号

Here's how it applies to your scenarios:

• Multiple browser tabs: When each tab initiates a connection to a web server (port 80), your operating system assigns a unique, temporary source port to each connection. Even though the destination IP/port are the same, the source port is different for each tab's connection. The OS uses this full four-tuple to route incoming responses to the correct socket, and the browser itself keeps track of which socket is tied to which tab's request (it maintains a mapping between connections and the tab/request context).
• Multiple browsers: Same logic applies! Each connection from any browser (Chrome, Firefox, Edge, etc.) gets its own unique source port assigned by the OS. So even if two different browsers are connecting to the same server on port 80, their four-tuples will differ thanks to the unique source ports. The OS routes the response to the correct browser's socket, and each browser handles its own connections internally.

It's like having multiple phone calls to the same office number (destination port 80)—each caller has a unique phone number (source port), so the office (server/OS) knows who to route the call back to.

内容的提问来源于stack exchange，提问作者Alberto