SENSE vs SYN Flood ??
I'm still trying to figure out why my internet connection is either extremely slow or not working at all while SENSE is protecting my devices. I checked the router firewall log, and looks like this, what is my SENSE router (192.168.0.4) doing?
Sorry for my reply.
Because there maybe indeed something as trouble based on SENSE-router.
But .... also based on Google Search -> some of provided IPs ((at least, two of first ones)) related with AVG (?!); Does there possible that Firewall (by AVG) or their another software installed under your devices.
Or with another layer of network - there can be any security features as DDOS-protection or so?
If some of this "technologies" detected SENSE connection (check URL/website ratings/analyzing) as something suspicious - maybe they block it/ban it (for some time)?
AVG PC TuneUp is the only product from AVG that is installed in few machines, and it does not have a firewall function in it. Instead, Norton Security is still in every machine, could that be the reason...?
Just as clarification -> I'm also only F-Secure user and this is only my own suggestions; Good if there will be normal and proper official response from F-Secure SENSE team (who definitely know how it works and about potential troubles);
Maybe - as it was suggested - you able to re-check with temporary "disable"-status (or so) for Norton Security (or potentially related features);
Based on your another topic: https://community.f-secure.com/t5/F-Secure-SENSE/SENSE-whines-about-no-connection/td-p/96330
Where you noted "Cisco cable modem (EPC3825 Eurodocsis 3.0 / Sonera)" - I able to think that you able to re-check this point too;
Based on brief Google Search --> it possible that this certain unit can be as modem/router (?!) and with certain features (which can be activated or not) like DDOS protection and other 'firewall'-rules;
Also not clear - your information about "SYN Flood" under logs - comes from ?!?!;
I think that "this one who marked it as "SYN Flood" situation" -> most likely able to prevent "src" (SENSE Router - as I able to understand) to do this; And block/ban temporary or globally; More looks as "false positive" about SENSE design activities;