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Very odd issue - IPv6 Firewall causing unbearable packet loss?

     Ever since moving my services to a new address two weeks ago, I've had intermittent outages and packet loss. I brought over my equipment from my last residence (Technicolor CGM4140COM Gateway) and performed a successful self-installation. Working in IT, I naturally have been trying to resolve this on my own rather than deal with technical support. I started with the obvious gateway reboots and factory resets with no success.

     Next came the speed tests. I have the Ultimate Internet Package with 300mbps down and 30mbps up, and all tests are run from a Windows 10 PC connected via ethernet. When the internet is working as it should I am getting >300mpbs down and >30mpbs up, sometimes way more. It really is phenomenal when it wants to work. When I noticed slower speeds, speed tests were showing ~250mbps download and LESS THAN 2MBPS upload speeds. Latency during these periods varied from 5ms to 300ms. After finding no outages in my area for a few days that would explain the issue, I knew this was getting technical. When playing online games and using VoIP services, I received endless packet loss errors. I decided to run pingplotter to track packet loss to www.google.com, and over a 12 hour period I averaged about 15% packet loss. During these "outages", packet loss ranges from 5% - 40% and at times the internet service is completely dropped. My first thought was congestion/interference to the wiring, but the router is showing a perfect signal strength for both upstream and downstream traffic at all times.

     Eventually, I came across the Firewall Logs in the gateway management portal. They showed the following errors that correlate EXACTLY to the times that outages begin: "FW.IPv6 INPUT drop , 48 Attempts - Firewall Blocked" "FW.IPv6 FORWARD drop , 214 Attempts - Firewall Blocked". The more severe the outage, the higher the "Attempt" number seems to be. I ran a test on IPv6-test.com which returned a 17/20 score that said: "Your router or firewall is filtering ICMPv6 messages sent to your computer. An IPv6 host that cannot receive ICMP messages may encounter problems like some web pages loading partially or not at all.". Disabling the IPv6 Firewall in the router completely does not resolve this AT all. It continues to block the messages regardless of the firewall configuration.

     A Cox technician visited today, but didn't seem to really know at all what I was talking about or what to do, and the service happened to be working fine when he arrived. He replaced the gateway with the same exact model today. It worked fine for a few hours, but it is now showing heavy packet loss exactly as the last one, and IPv6-test.com shows the same score and error. The firewall logs of the new gateway show the exact same firewall blocks, so a bad gateway is out of the question. I'll attach all the relevant information I can, but I have absolutely no idea where to go with this issue. The gateway replacement has not solved the issue at all. It seems beyond my control, but I can't get ahold of anyone from Cox who is knowledgeable enough about these types of issue to actually try and fix the issue. 

As a result of my unreliable connection for the past few weeks, I've had to stay after work to complete homework for my college courses. So far I've been able to track and log about 7 hours of downtime within the past 6 days, but I'd say I get about 10 hours of reliable service per day. Which is unacceptable. I'm only 20 years old and I can't continue to dedicate so much time to fixing this, especially when I'm paying so much for solid internet.

UPDATE AS OF 7/6 5PM: Last evening (7/5) at around 5pm, my internet was running with about 50% packet loss. It was completely unusable, and the outage persisted until about 4am. About 11 hours straight of downtime. Luckily I was able to use my mobile hotspot to submit my work on time. Today (7/6), the second service tech arrived. He was much more knowledgeable about the issue, and here's what went down. He said that there was a 15ft coax cable FROM THE MAIN LINE rolled and bundled up in an outside shed, and this line fed into the main box of my apartment. He said that with the line being bundled up, it was likely that I was experiencing intermittent issues as a result of the interference this caused. Another issue he found, was the splitter/wire configuration. The main line was run through a very old 3-way coax splitter, which led into ANOTHER old 3-way splitter. Another odd quirk was that for every coax connection in the apartment (4-5), there were two coax lines run... goes to show how well this apartment was wired up. It's been about 4 hours since he's cleaned everything up, and everything's working normal so far. Time will only tell if this resolves the problem. It's worth noting, ipv6-test.com shows the same IPv6 ICMP Firewall issues, and the modem Firewall log is still reporting the input and forward drops. Fingers crossed.

UPDATE AS OF 7/7 10PM: The issue has not been fixed at all. After a modem replacement, and a complete rewire in my apartment, the internet is still dropping out, and it seems to mostly happen at night. I don't think it's traffic related, as it gets even worse in the early hours of the morning. I have posted updated network monitors that show the packet loss from last night and tonight, both taking place after the two tech visits.

PingPlotter Traceroute Results (7/6-7/7)

PingPlotter Traceroute Results (6/29-7/4)

Gateway/Connection Data