Network Basics

网络协议解析

最新推荐文章于 2025-12-02 15:16:40 发布

原创最新推荐文章于 2025-12-02 15:16:40 发布 · 106 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#运维 #网络

本文解析了浏览器从输入URL到页面展示的全过程，包括DNS解析、TCP连接建立与HTTP请求响应流程。详细介绍了DNS递归与迭代查询机制，TCP的可靠传输特性及三次握手过程，并对比了TCP与UDP的不同。

1. What happens after you typing an URL into your browser

Browser contacts with the DNS server to find out the IP address of URL
DNS server return the requested IP address
Browser builds up and connects with web server by TCP at port 80
Browser send the http request to the server and server return the html code to browser
Browser renders the display result of html code
Browser terminates the connection when window is closed

2. DNS

Check if the URL has already been cached. If so just return the result (local Resolver)
Preferred DNS server will query other DNS server RECURSIVELY / ITERATIVELY

3. TCP & UDP

Transmission Control Protocol is a connection-oriented network protocol

Reliable: When you send a message by TCP you will know it will get there. If it or some parts of it lost on the way the server will re-request the lost part.
The order is guaranteed by the sequence number
HeavyWeighted: all the out of order parts will be re sent

User Datagram Protocol is a connectless network protocol

You don't know whether you message is delivered
You don't know the order of your sent message
Light Weighted: No ordering information, no tracing information. It's faster

TCP Handshake Process

Client sends a SYN to server with a segment sequence number
Server replies client a SYN-ACK with the client sequence number + 1 and its sequence number
Client send ACK to server with server sequence number + 1

Now both client and server receive an acknowledgement of connection. The communication is established.

Reliable Delivery

For each TCP packet receiver must send acknowledgement to show it is delivered. If the sender doesn't receive the acknowledgement sender will resend the packet until acknowledgement received.

Flow Control (TCP sender's/Receiver's Window)

A TCP window is the number of data that sender can send before it gets the acknowledgement.

Congestion Control

congestion window