网络基本功（二十八）：Wireshark抓包实例分析HTTP问题(下)

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 

 

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.

 

 

如下示例是一个简单的客户端报错。按照如下步骤进行操做：

1. 右键有报错的报文。

2. 选择Follow TCP stream，会看到如下窗口：

   3.  显示如下内容：

• 客户端尝试浏览URI/poker-client/broadcast.htm（如截屏中1和3所示）

• URI经过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）可能有多种缘由。如下示例是一个小办公室碰到的问题：员工可以访问Facebook，但当他们点击站点上的连接，则显示页面被拦截。如下截屏中，可看出页面被防火墙拦截：

 

工做原理:

标准的HTTP浏览模式以下：

1. TCP打开链接（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链接的状况下（大多数网页都是如此）。每一个链接须要一个DNS 查询，响应，TCP SYN-SYN/ACK-ACK，以及HTTP GET。以后数据才会出如今显示屏上。

 

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，会看到链接的细节数据。另外一个普遍应用的工具是Fiddler，Fiddler是HTTP故障排查的免费工具。