Advise on some issues with IPv6

[Logi]

I have TMHI, initially I was using their Gateway (Sagemcom) and I think it is configured with IPv6 Passthrough, I have my own Asus Router (AX88U) connected to the TMHI Gateway, I have IPv6 in the Asus configured as Passthrough as well, and every time the Sagemcom reboots (planned or unplanned) my clients (on the Asus Router side) start having issues with IPv6, I think it might be related to that TMHI only provides 1 IPv6 address/DHCPv6 PD?

If I check the clients having issues, I noticed the number of IPv6 addresses assigned start to increase, I have to disconnect them from the network, so they will refresh their IPs (4 and 6) and all is good again, for a while, until the next restart on the TMHI gateway, sometimes is not even a restart, maybe TMHI CGNAT/DHCPv6 server will assign a new IPv6 and the problem starts again. Is this an issue with the Asus Router and IPv6 Passthrough? I don't think so, but checking in.

I have now, a third part gateway, to replace the TMHI provided gateway (Sagemcom), it has the capability to be configured with Passthrough and NAT6, initial tests in Passthrough mode, provided the same results/issues as with the Sagemcom, do you think changing the third party gateway IPv6 configuration to NAT6 might help solve the issues?

 

[Crimliar]

TMHI? T-Mobile Home Internet?
If so then in the UK, they used to supply a 64 bit prefix "native" IPv6 connection and the IPv4 used to be CGNAT. So if this is T-Mobile, then try switching to Native IPv6 mode with a 64 bit prefix. Next up, on your connected devices, you've told us what is happening, but you've not told us about the problem(s) this is causing! If you can get your global IPv6 addresses allocated locally from the prefix, you also get into the realm of having local IPv6 addresses too (may need to change a setting on your devices), and in addition another local and global IPv6 address for each device generated from the prefix and the devices individual MAC address. So it's not uncommon for each device to have at least four active IPv6 addresses. Far less than on IPv4, devices may discard the old non-MAC IPv6 addresses in favour of a new one each time their connection is refreshed or they are powered on!

 

[Logi]

Yes, this is T-Mobile Home Internet US, I tried the Native option on the third-party gateway, didn't work when checking with https://test-ipv6.com/, maybe here they use a different configuration.

The problem I have is that when IPv6 addresses start piling up with every gateway reboot connectivity on the client devices is unreliable, slowness, etc.

 

[Analog-1]

If your using IPv6 passthrough on both devices be advised your public IPv6 connection will have no firewall and will be open to the internet.

 

[Logi]

If your using IPv6 passthrough on both devices be advised your public IPv6 connection will have no firewall and will be open to the internet.

Thank you for the information, will NAT6 on the TMHI Gateway (Third party gateway) and Passthrough on the Asus Router will be the correct and secure configuration?

I think the T-Mobile provided gateways are configured with NAT6 but I am not sure

 

[Analog-1]

I think the T-Mobile provided gateways are configured with NAT6 but I am not sure

Not sure myself never used TMHI.