Flint3 Dual WAN failover test-ipv6.com showing IPV4 from main WAN and IPV6 from failover

Routers
1

Let me start by saying I don't know much about IPV6.

I have dual WANs connected to my Flint3 in failover mode, Comcast as primary through the WAN interface, and T-Mobile Home as backup through the USB/Tether interface with a USB NIC connected to their gateway.

If I enable IPV6 in passthrough mode, https://test-ipv6.com/ says I have an IPV4 address through Comcast and an IPV6 address through T-Mobile. Also, the guest network no longer has internet access.

If I try Native or NAT6 modes, I lose internet. (I think Guest always uses NAT6).

What is wrong here? Thanks.

Edit: I just noticed in Luci status page under network, it lists my comcast IPV4 upstream, then T-Mobile IPV4 upstream, then T-Mobile IPV6 upstream, then Comcast IPV6 upstream. Why is it putting T-Mobile IPV6 first?

Edit2: If I switch the tethering interface to be higher priority in multi-wan failover than the WAN connection, then the IPV4 and IPV6 addresses switch. T-Mobile IPV4 and Comcast IPV6. If I disconnect the tethering interface, everything works, including the guest network, and I no longer lose internet if I set native or nat6 mode, although the test only passes with it in passthrough..

I should also note it does this after a factory reset, just connecting the tethering interface and turning on IPV6, and it's on 4.8.1

3

Hi

Considering that you are using a WAN connected to a main router, and Tethering for cellular, it is normal to only provide you with IPv6 access in pass-through mode, as these two ways normally does not provide IPv6 PD prefix, preventing Flint 3 from creating its own subnet.

For priority issues, try checking the IPv6 routing table on the client device, which may depend on its priority (and the time in which the corresponding address was obtained).
For Windows, run the following command via CMD:

route -6 print

For MacOS, execute the following command via Terminal:

ip -6 route
4

Thank you for the response. I'm not tethering to a cell phone, I've connected a USB NIC to the Flint3, which is eth2 and shows up as "tethering" in the Flint3.

It can't only work in passthrough, as the guest network always apparently uses NAT6. Like I said, NAT6 works fine as long as only one WAN connection is present but dies when the other is connected.

The priority issue is not a client side issue, it's the router itself. It doesn't matter which client I try, In failover mode with "tether" set lower priority, the router is correctly putting eth0 (WAN) before eth2 (USB/tether) for IPV4, but for IPV6 it's putting eth2 (USB/tether) before eth0 (WAN).

If I put "tether" (eth2) as higher priority than WAN (eth0) in failover, then they switch. The router lists eth2 (USB/tether) before eth0 (WAN) for IPV4, and eth0 (WAN) before eth2 (USB/tether).

5

Thank you for the update, and apologies for the delayed response—we’ve just returned from the National Day holiday.

Let me try to explain further.

  1. NAT6 is only works when the WAN port has an available IPv6 address (not Link-Local Address, i.e., addresses starting with fe80). Therefore, please verify whether your ISP provides an available address for the WAN. (Some ISPs only provide IPv6 PD and do not provide another available address for the WAN.)

  2. In Native or Passthrough mode, LAN client devices will directly obtain public IPv6 addresses. This means they will select their own source addresses, and the router will forward traffic to the corresponding ISP based on these selected source addresses and doesn't modify the source address (NAT).

  3. If you wish to manage exit links via Multi-WAN, configure the router's IPv6 mode to NAT6. Additionally, as mentioned above, ensure both ISPs provide usable IPv6 addresses for the WAN port. Note: After adjusting priorities in the current version, a router reboot is required for changes to take effect. We are aware of this issue and plan to address it in a future release.