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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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