# 網絡基本功（二十八）：Wireshark抓包實例分析HTTP問題(下) **轉載請在文首保留原文出處：EMC中文支持論壇**[https://community.emc.com/go/chinese](https://community.emc.com/go/chinese) [](https://community.emc.com/servlet/JiveServlet/showImage/2-870583-108192/image001.gif) ## 介紹 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. | 以下示例是一個簡單的客戶端報錯。按照以下步驟進行操作： 1. 右鍵有報錯的報文。 2. 選擇**Follow TCP stream**，會看到以下窗口： [](https://community.emc.com/servlet/JiveServlet/showImage/2-870583-108193/image002.jpg) 3. 顯示以下內容： * 客戶端嘗試瀏覽URI/poker-client/broadcast.htm（如截屏中1和3所示） * URI通過[http://www.888poker.com/poker-client/promotions.htm轉發（截屏中2](http://www.888poker.com/poker-client/promotions.htm轉發（截屏中2)所示） * 狀態碼為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）可能有多種原因。以下示例是一個小辦公室碰到的問題：員工能夠訪問Facebook，但當他們點擊站點上的鏈接，則顯示頁面被攔截。以下截屏中，可看出頁面被防火墻攔截： [](https://community.emc.com/servlet/JiveServlet/showImage/2-870583-108194/image003.jpg) **工作原理:** 標準的HTTP瀏覽模式如下： 1. TCP打開連接（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連接的情況下（大多數網頁都是如此）。每個連接需要一個DNS 查詢，響應，TCP SYN-SYN/ACK-ACK，以及HTTP GET。之后數據才會出現在顯示屏上。 當你在packet detail面板沒有看到顯示內容時，右鍵報文并選擇Follow TCP stream，會看到連接的細節數據。另一個廣泛應用的工具是Fiddler，Fiddler是HTTP故障排查的免費工具。 ## 參考 Network Analysis Using Wireshark Cookbook