Powerlines and Firewalls - A strange coincidence of high security and LAN disconnections

This article is about a connection problem of TP-LINK powerline adapters, seemingly solved with a rather strange solution!

Before I get to that, let me describe how I am using my powerline adapters: 

I have a small home network of computers, smartTVs and cameras, served over 4 powerline adapters: a pair of TL-WPA4220 adapters along a pair of  rather old TP-LINK-TL-PA211-AV200's.
 
I am not using Wifi, because I have two small kids and no need to risk their health with possible implications of high frequency transmitters near them. Also, as our rooms are far away located, installing normal CAT5-6 LAN cables demands ruining the walls. So my only viable option is powerline adapters.

My four powerline adapters were working fine with each other for over four years, providing my home with an almost cable-quality LAN. Speeds were up to 140mbps between the two old adapters and around 260mbps between the two new ones. These are maybe not great to transfer large files, but are perfect to provide mine and my wife's work PC's with fast Internet access, allowing at the same time my two daughters watch their favorite kid animations on the family smart TV in FullHD.

The only problem since I bought these adapters, was in 2013, after over one year of using them. Some time, each of my two PA211 adapters had their main capacitors blown. Practicing my electronic skills I replaced the capacitors with new (and total cost not over an euro). They are working since.

But ...not so perfectly! Some days ago I met with a strange disconnection problem. Internet  constantly dropped, a lot of times each hour, and with no apparent reason!

I tried hard to find the source of the problem, to no avail. I checked the adapters, and they had no visible problems. I disassembled them, still finding no problems. I checked my router internet connection, and found nothing strange there too. I checked any setting of my PC's I could think of in Windows and Linux, and found no collisions or miconfigurations. I checked at my network data flow and found no problems there. There was also no problem caused by the DCHP server. I worked many hours with the tool TP-Link  provides for powerline management (tpPLC) but...

All these had a great negative effect on my nerves, as they probably have with any other people experiencing similar problems.

So, what was causing the connection problems?

After many hours of reading forum posts about similar problems, and after long hours of tiresome experimentation, I seem to have found it:  It is not the power save facility of the adapters as some people are saying. It's not electric interference by other equipment, as some others argue.

The problem seems to be caused by something rather unexpected, as my router's ...firewall!

My router is a sturdy ZTE ZXHN H168N router, which still works after 3 years of abuse and brutal experimentation. It kept its connected status even under my most evil internet experiments.

As I said, it kept its connection alive even as the powerlines stopped working, as I could connect with Internet under Wifi the same time the powerlines were refusing to do. So I had no real reason to believe the router was causing the problem! 

But, as I realised two days before today, the only thing I wasn't suspecting was the setting of my router's firewall to its highest security level, a setting I changed one week before the problem appeared!

This didn't seem to present problems in any other way, so I wasn't expecting it could affect the powerline connections! But apparently, it did! I changed it back to "middle security" and the connection quality returned back to perfect again!

It may be a coincidence. But, my experience says otherwise.

So, all you having similar problems, please try to change your router firewall to some lower security setting. It may solve your problems.

If it does, please leave a message confirming my -supported by the facts until now- hypothesis.

You may ask, of course, how is possible for a firewall setting to affect powerline performance?

Presently, I cannot think of an answer, as the only change on the firewall on "high security" is the refusal to answer outside (WLAN) "pings". Why would this affect my inner LAN connections?

This may be answered in some future post...