Strange issue with IP allocation and stability

So, bit of a strange issue here, I'm not even sure which forum to put it in.

Been using 4G from SMARTY (Three network) as my home broadband for 2 weeks, it's working really well with most websites and services. Some websites seem to have issues with loading content in the background (ie. Twitch.tv will buffer every minute or so, despite a stable 50Mb/s connection), which goes away when using a VPN. I assumed it may be down to the public IP address changing (something that cannot be disabled), so I created a small test site to track changes to the IP (can be viewed here).

It seems the IP address changes with pretty much every single new connection (ie, every 1 second or so), which is a lot more frequent than I would have expected. Keepalive seems to keep sessions open with the same IP for about 30 seconds. Is this normal and expected behaviour with LTE?

Second part, it appears that on all desktop browsers (Chrome, Edge & Firefox) that background AJAX requests frequently have issues, either timing out or failing due to 'ERR_CONNECTION_RESET'. Interestingly, Chrome on Android does not have this issue at all, connected to the same 4G router via WiFi. Any ideas what's going on and how this could be resolved (without needing to connect to a VPN 24/7)?

Screenshots:
Desktop (Chrome): https://i.imgur.com/Tr4slDE.png
Android (Chrome): https://i.imgur.com/a2ExPrH.jpg (via WiFi, using same 4G SIM & connection)
Twitch network debugging: https://i.imgur.com/oI3VEX0.png

EDIT: The timeouts seem to occur quite less often when testing with another desktop PC, it seems my PC may be the culprit. No ideas on why, as using a VPN or alternate WAN connection makes the problem go away.

Edited by thebigdolphin1 (Thu 12-Aug-21 22:56:43)

Okay, disregard - I'm confident this is an issue with my Windows installation or NIC driver. Other PCs (and even a linux distro on the same machine) don't experience these timeouts or connection failures. If anyone has any ideas on what could be the cause, please do let me know as I still haven't found a fix.

That internet connection is *not* normal or stable. A public IP address that is changing on every page connection attempt and/or every single second is categorically not behaving correctly.

Clearly your machine when running windows is having issues with it. The other machines and OS's appear to be able to "paper over the cracks" in the poor quality of the connection.

You may be able to tweak some setting on your windows box to help, perhaps increasing the MTU size for example, but the root cause appears to be the erratic/unstable public IP address allocation.

I'll have to put the SIM in my phone and try a different mast to see if it's just a local Three issue, though after speaking to some others it seems Three/SMARTY aggressively reassign IP addresses. Worth noting that once a connection has been established, the connection retains its public IP for the rest of its lifetime, its just each connection may have different public IPs independent from each other. I've noticed it causes a few problems with sites that log you out on IP changes, or CDNs that host content using an IP-based policy.

I have a feeling it's something to do with my NIC's driver software, they put a bunch of QOS stuff in there and I can't seem to find a generic driver that fixes the problem. Unfortunately I can't find much online as it's now a discontinued product.

Badly configured (CG)NAT can result in a different IP for every new connection, it does help distribute client traffic but breaks many services, most notably Sky on-demand.

Three seem to have a lease time of one minute so renew every 30 seconds, using the 3internet APN to obtain a public IP the address is mostly renews successfully whilst the LTE connection is established, infrequently the renewal is NAKed and a new address assigned.

What happens when you use a different APN?

Others may know better but I can't see how an issue on your LAN would cause the WAN IP to change.

Can't be done with SMARTY, they manually override the APN (you can enter any value and it works the same).

I'm not suggesting the local NIC is causing the IP to change, but that it's the reason connections keep timing out or dropping on my machine. The WAN IP obviously changes to Three's IP assignment policy, but no other devices seem to share the connection issues.

In reply to a post by thebigdolphin1:

I have a feeling it's something to do with my NIC's driver software, they put a bunch of QOS stuff in there and I can't seem to find a generic driver that fixes the problem. Unfortunately I can't find much online as it's now a discontinued product.

What's the TCP offload setting for the NIC driver (not the same as Windows)?

Heh, forgive me a little here but this is going into territory I'm not familiar with. Looking at the NIC's device properties, 'TCP Checksum Offload (IPV4)' (I assume that's what you're after?) is set to 'Rx & Tx Enabled'.

Yep set to 'Disabled'. Also set Large Send Offload V2 (IPv4) to 'Disabled'.

Reboot machine. Go back to these settings and ensure settings have remains disabled.

Test again