In some cases, problems can occur before requests reach SharePoint. To investigate such problems, you may need to capture and analyze network traffic or IIS requests. The following tools can used for various network tracing tasks:
For example, you can:
IIS Failed Request Tracing
Even when a network request makes it to a WFE server, there are still a wide range of conditions that could prevent IIS from being able to parse the request and pass it to SharePoint. These conditions could include incorrectly configured site bindings, configuration errors in the Web.config file, missing IIS modules, authentication failures due to loopback checking and so on. Failed request tracing in IIS enables you to capture detailed information about requests as they move through the IIS pipeline. IIS 7, IIS 7.5 and IIS 8.0 use a rule-based approach to failed request tracing. At a high level, you must complete the following tasks:
  1. In IIS Manager, enable failed request tracing for the IIS website that hosts your SharePoint web application.
  2. Configure failed request tracing rules to define the error conditions you want to log. These can include specific HTTP status codes, requests that take longer than a specified time and minimum event severity levels.
  3. Specify the trace provider and the categories that you want to log. Depending on where in the request pipeline you are experiencing areas, you might include the ASPNET, ISAPI Extension, or WWW Server trace providers.

After you configure failed request tracing, detailed information about any requests that meet the criteria specified by your failed request tracing rules is written to a log file. By default, these files are stored in the %systemdrive%\inetpub\logs\FailedReqLogFiles\W3SVC1 folder.