404 file not found，那就是rewrite的rules配的有问题，这里有篇官方文档，读完了就不会犯这种错啦。
https://docs.microsoft.com/en-us/iis/extensions/url-rewrite-module/url-rewrite-module-configuration-reference
500 server internal error，这个其实一般用ASP.NET才会遇到，尤其是MVC。。因为@Html.ActionLink之类的函数，在渲染的时候会和url rewrite冲突，报错为：
Cannot use a leading .. to exit above the top directory.
<li>@Html.ActionLink("Home", "Index", "Home")</li>
=>
<a href="/Home/Index" class="navbar-brand">Home</a>
还有种情况就是rewrite成功，返回了200，但是却不是自己想要的结果，如果不能正向找到问题，那就把这段配置加到system.webServer节点中去，抓去所有返回200-299的访问，然后访问下网页，再看看生成W3SVC的日志。日志生成后，记得把这段配置删了，不然会非常卡，原因你懂的。
<tracing> <traceFailedRequests> <remove path="*" /> <add path="*"> <traceAreas> <add provider="ASP" verbosity="Verbose" /> <add provider="ASPNET" areas="Infrastructure,Module,Page,AppServices" verbosity="Verbose" /> <add provider="ISAPI Extension" verbosity="Verbose" /> <add provider="WWW Server" areas="Rewrite,RequestRouting,Authentication,Security,Filter,StaticFile,CGI,Compression,Cache,RequestNotifications,Module,FastCGI" verbosity="Verbose" /> </traceAreas> <failureDefinitions statusCodes="200-299" /> </add> </traceFailedRequests> </tracing>
下面再来一个抓访问慢的请求发生时的dump文件的配置
<tracing><traceFailedRequests><remove path="*" /><add path="*" customActionExe="d:\home\site\Diagnostics\procdump.exe" customActionParams="-ma -accepteula %1% d:\home\site\Diagnostics\w3wp_PID_%1%_" customActionTriggerLimit="5"><traceAreas><add provider="ASP" verbosity="Verbose" /><add provider="ASPNET" areas="Infrastructure,Module,Page,AppServices" verbosity="Verbose" /><add provider="ISAPI Extension" verbosity="Verbose" /><add provider="WWW Server" areas="Authentication,Security,Filter,StaticFile,CGI,Compression,Cache,RequestNotifications,Module,FastCGI" verbosity="Verbose" /></traceAreas><failureDefinitions timeTaken="00:00:30"/></add></traceFailedRequests></tracing>
@Html.ActionLink
原文：https://www.cnblogs.com/nicklooo/p/9265535.html