Just to be clear here, Fiddler doesn't "send traffic" to itself; it's up to the client to send traffic to Fiddler. Typically, this works automatically, because the client picks up the system proxy settings (which Fiddler sets) and respects them.
If Fiddler is unable to set the system proxy (e.g. because there's security software that prevents it, or other software that immediately overwrites its changes) then traffic will not be sent to Fiddler, but the "Echo" page will remain available at http://127.0.0.1
. You can see what proxy is currently configured by choosing Tools > WinINET Options > LAN Settings inside Fiddler or Tools > Internet Options > Connections > LAN Settings inside IE.
Another case occurs when the system's proxy setting logic is broken and the settings cannot be changed. To check for that, without Fiddler running, go to the LAN Settings and configure a bogus proxy (e.g. http://bazinga
on port 9999). Click OK on the dialogs and then reopen them. If the settings weren't preserved, then the system APIs are broken. This could be a result of a bug in the OS, or VPN software, or malware, or any host of other similar issues.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.