Fix Google Security Code

Google Security Code (http://g.co/sc) is one type of 2-step verification. This is particularly useful when security keys and passkeys are not available.

I have been using it in my LXC containers, until today I found out that it stopped working. It just kept saying "The code is invalid".

It is easy to rule out some factors:

The code works on other browsers on my laptop.
The code works on other devices that are directly connected to the router.

So it appears that Google also checks IP addresses besides the security code. Recently I have IPv6 enabled, so most devices that are directly connected to the router have both IPv4 and IPv6 addresses. But I only enabled IPv4 for my LXC containers.

So I guess when a code is generated by device A and used by device B, Google should be able to check that device A and device B are closely located. But in my case, IPv6 address appears on device A but not on device B, which may look suspicious.

To fix the problem, I just needed to disable IPv6 on my laptop before generating the code. Then Google would accept the login from the LXC contanier.

I hope Google can show some hints in the error messages, at least mention that I should check the network settings.

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