# 网络基本功（二十八）：Wireshark抓包实例分析HTTP问题(下) **转载请在文首保留原文出处：EMC中文支持论坛**[https://community.emc.com/go/chinese](https://community.emc.com/go/chinese) [](https://community.emc.com/servlet/JiveServlet/showImage/2-870583-108192/image001.gif) ## 介绍 本文承接上文。 ## 更多信息 **Client errors:** |  **Code**  |  **Status**  |  **Explanation**  |  **What    to do**  | | --- | --- | --- | --- | | 400 | Bad   request | The   request could not be understood by the server due to a syntax problem.   The request should be modified by the client before resending to it. | Check the   website address. This can also happen due to a site error. | | 401 | Authorization   required | The   client is denied access due to the lack of authentication codes. | Check   your username and password. | | 402 | Payment   required | Reserved   for future use. | | 403 | Forbidden | The   client is not allowed to see a specific file. This can be due to the server   access limit. | Check the   credentials. Also, there are fewer chances that the server is loaded. | | 404 | Not found | The   requested resource could not be found. | This can   be because the resource was deleted, or it never existed before. It can also   be due to URL misspellings. | | 405 | Method   not allowed | The   method you are using to access the file is not supported or not allowed by   the resource. | | 406 | Not   acceptable | Content   generated by the resource is not acceptable according to the client request. | Check/update   your browser. | | 407 | Proxy   authentication required | Request   authentication is required before it can be performed. | The   client must first authenticate itself with the proxy. | | 408 | Request   timed out | It took   the server longer than the allowed time to process the request. | Check   response time and load on the network. | | 409 | Conflict | The   request submitted by the client cannot be completed because it   conflicts with some established rules. | Can be   because you try to upload a file that is older that the existing one or   similar problems. Check what the client is trying to do. | | 410 | Gone | The URL   requested by the client is no longer available from that system. | Usually   this is a server problem. It can be due to a file that was deleted or   location was forwarded to a new location. | | 411 | Content   length required | The   request is missing itsContent-Length header. | Compatibility   issue on a website. Change/update your browser. | | 412 | Precondition   failed | The   client has not set up a configuration that is required for the file to be   delivered. | Compatibility   issue on a website. Change/update your browser. | | 413 | Request   entity too long | The   requested file was too big to process. | Server   limitation. | | 414 | Request   URI too long | The   address you entered was overly long for the server. | Server   limitation. | | 415 | Unsupported   media type | The file   type of the request is not supported. | Server   limitation. | 以下示例是一个简单的客户端报错。按照以下步骤进行操作： 1. 右键有报错的报文。 2. 选择**Follow TCP stream**，会看到以下窗口： [](https://community.emc.com/servlet/JiveServlet/showImage/2-870583-108193/image002.jpg) 3. 显示以下内容： * 客户端尝试浏览URI/poker-client/broadcast.htm（如截屏中1和3所示） * URI通过[http://www.888poker.com/poker-client/promotions.htm转发（截屏中2](http://www.888poker.com/poker-client/promotions.htm转发（截屏中2)所示） * 状态码为404 Not Found（如截屏中4所示） **Client errors:** |  **Code**  |  **Status**  |  **Explanation**  |  **What    to do**  | | --- | --- | --- | --- | | 500 | Internal   server error | The web   server encountered an unexpected condition that prevented it from   carrying out the client request for access to the requested URL. | Response   that is usually caused by a problem in your Perl code when a CGI program is   run. | | 501 | Not   implemented | The   request cannot be executed by the server. | A server   problem. | | 502 | Bad   gateway | The   server you're trying to reach is sending back errors. | A server   problem. | | 503 | Service   unavailable | The   service or file that is being requested is not currently available. | A server   problem. | | 504 | Gateway   timeout | The   gateway has timed out. This message is like the 408 timeout   error, but this one occurs at the gateway of the server. | Server is   down or nonresponsive. | | 505 | HTTP   version not supported | The HTTP   protocol version that you want to use for communicating with the server is   not supported by it. | Server   does not support the HTTP version. | 服务器不可用（错误代码503）可能有多种原因。以下示例是一个小办公室碰到的问题：员工能够访问Facebook，但当他们点击站点上的链接，则显示页面被拦截。以下截屏中，可看出页面被防火墙拦截： [](https://community.emc.com/servlet/JiveServlet/showImage/2-870583-108194/image003.jpg) **工作原理:** 标准的HTTP浏览模式如下： 1. TCP打开连接（三路握手信号） 2. HTTP发送GET命令 3. 数据下载到浏览器 在一个网页打开多个连接的情况下（大多数网页都是如此）。每个连接需要一个DNS 查询，响应，TCP SYN-SYN/ACK-ACK，以及HTTP GET。之后数据才会出现在显示屏上。 当你在packet detail面板没有看到显示内容时，右键报文并选择Follow TCP stream，会看到连接的细节数据。另一个广泛应用的工具是Fiddler，Fiddler是HTTP故障排查的免费工具。 ## 参考 Network Analysis Using Wireshark Cookbook