網絡基本功（二十八）：Wireshark抓包實例分析HTTP問題(下)

網絡基本功（二十八）：Wireshark抓包實例分析HTTP問題(下)

 

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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.

 

 

如下示例是一個簡單的客戶端報錯。按照如下步驟進行操做：

1. 右鍵有報錯的報文。

2. 選擇Follow TCP stream，會看到如下窗口：

   3.  顯示如下內容：

• 客戶端嘗試瀏覽URI/poker-client/broadcast.htm（如截屏中1和3所示）

• URI經過http://www.888poker.com/poker-client/promotions.htm轉發（截屏中2所示）

• 狀態碼爲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.

 

服務器不可用（錯誤代碼503）可能有多種緣由。如下示例是一個小辦公室碰到的問題：員工可以訪問Facebook，但當他們點擊站點上的連接，則顯示頁面被攔截。如下截屏中，可看出頁面被防火牆攔截：

 

工做原理:

標準的HTTP瀏覽模式以下：

1. TCP打開鏈接（三路握手信號）

2. HTTP發送GET命令

3. 數據下載到瀏覽器

 

在一個網頁打開多個鏈接的狀況下（大多數網頁都是如此）。每一個鏈接須要一個DNS 查詢，響應，TCP SYN-SYN/ACK-ACK，以及HTTP GET。以後數據纔會出如今顯示屏上。

 

當你在packet detail面板沒有看到顯示內容時，右鍵報文並選擇Follow TCP stream，會看到鏈接的細節數據。另外一個普遍應用的工具是Fiddler，Fiddler是HTTP故障排查的免費工具。