Filtering loopback traffic

[Bucky Kid]

HI, without having changed anything all of a sudden some, but not all applications refused to start or did not work. By selectively turning off CFW features I came to loopback filtering switch, which once turned off enabled again all network based applications to work, but the feature is off. Please tell if it's safe and if not, how to restore all applications connections with loopback filtering ON.

[futuretech]

I doubt anything stops working just for having loopback filtering enabled, unless you have rules to block connections to localhost/loopback. Always check the logs to see if anything is being logged as blocked.

[Bucky Kid]

The log was empty when I started the incriminated applications. And yes it's the loopback filtering switch making the difference.
Particularly the problems had Audition very long starting (probably waiting for net timeout), DeeMix not showing up but sitting in the background and doing nothing, and opening addon worker inspector in Firefox, which always asks for permission of incoming connection from 127.0.0.1 to 127.0.0.1, but with loopback filtering active not asking and showing empty window.
At first I switched CFW to bypass mode, which worked, then reverted back to safe mode and tried turning off things till the lb filter unlocked the traffic.
I have set some global rules but those mostly for enabling home network devices by MAC whitelist etc., no conflicts encountered with them. As I stated in OP, nothing changed in CFW config for ages, except making perapp rules for newly installed softwares. This unexpected blocking started very recently.

[futuretech]

I just don't see how having loopback filtering enabled would interfere with applications, unless the application needs to communicate with localhost, and you blocked it in the application rules. The global rules are not relevant with applications especially with loopback connections, you need to check your application rules to see if any block rule targeting the localhost is set.

Also what do you mean for firefox inspector? Do you mean this? https://developer.mozilla.org/en-US/docs/Tools/Browser_Toolbox

[aim4it]

It might if some 3rd party app/driver/security software was rerouting all traffic through the loopback zone for filtering like a proxy or vpn.  Might also explain why Comodo doesn't see the traffic.

[Bucky Kid]

Do you mean this? https://developer.mozilla.org/en-US/docs/Tools/Browser_Toolbox

Yes this, but not only application working limited with LB filtering.

Might also explain why Comodo doesn't see the traffic.

I'm occassionally using VPN as background agent, but even if not running, the LB filtering limits the communication. The VPN provider also kept full connectivity together with LB filtering before IT happened.

[Bucky Kid]

I've found an older exported configuration, which I restored and found it not undesirably blocking any connectivity. By comparing current broken and the older config snapshots, I've come to differing block which is defining exception addresses, by restoring the current config and locating the section in config dialogue (Webpage filter rules > Categories > Exceptions) , I've found numerous records there, many of them duplicate. I have no idea how these were added there as I was never asked to add exceptions and didn't add them by hand either. After I wiped out all exception addresses and saved the configuration, the traffic is  again working for all applications unrestricted. I wonder how these exceptions could block the traffic and how to prevent auto-adding them.