Sudden packet loss

Installing and Using OpenWrt
1

I have a Flint 2 MT-6000 router which I have had for nearly two years now.

It is plugged into a Virgin Media UK Super Hub 5 docsis cable modem router via Cat6 into its 2.5Gbit ethernet port. I have ran the SH5 in modem mode for 2 years, no issues at all.

Last Sunday I decided to flash the MT-6000 with Openwrt 25.12.2. I noticed immediately random packet loss. Only a couple of % but enough to cause disruption.

I thought it must be 25.10.2 so then flashed it back to 24.10.6, I know that works well and same again, sporadic packet loss. I did a complete factory reset too, no difference.

I flashed it with GL-iNets Openwrt 24 Beta and exactly the same issue.......

If I run the cable modem router in router mode, I get no packet loss. The IP changes though.

Virgin Media have sticky IP's so changing firmware on the Flint does not cause a new address to be issued.

I spotted a Reddit thread regarding packet loss on Openwrt and Virgin Media connections. I changed the Firewall settings to drop incoming instead of reject, made zero difference in this instance.

I can't see any activity on the MT6000 at all that would cause this disruption. I have checked the sys logs. Nothing stands out in the logs.

Any idea what could be causing it? Nothing has changed physically in terms of cabling.

All I change on the WAN side of the Flint is disable IPV6 and set the DNS to Cloudflare - I can't change the DNS on the cable modem router.

2

Have you tried connecting a computer directly to the modem (no router)? This will tell you if the issue is upstream of your MT6000 (namely the modem and/or the ISP, although you won't be able to determine which of those two).

3

I haven't, mainly because I am a bit concerned of the issue being caused by disruption on the WAN side. DDOS, Synflood etc.

4

It may be a bit disruptive, but a quick test is necessary to determine the location of the issue.

5

I ran pingplotter which highlighted an issue with Virgin Media.

The issue now appears to have resolved itself so my Flint is back on Openwrt.

6

Glad that it is now resolved. As I had mentioned, it was critical to test the upstream by removing the variables of your router (hardware and config).