I have a problem accessing websites secured by Cloudflare with my IPv6 prefix on work.
We noticed it a few weeks ago when a colleague was not able to access the login-page on gitlab.com. Gitlab itself works without a problem, but after clicking on “Login”, one gets stuck in a redirect loop “Checking your browser”.
We tried multiple devices and browsers, but without any success.
Together with our IT support, I analyzed the network configuration and traffic, but everything looks okay. The server responds in a normal way. Then we learned that the problem is solved by disabling IPv6. Using IPv4, everything works normally, I get directed to the login page within a few seconds, with IPv6 one gets directed after ~12 minutes. But IPv6 is necessary for the work.
The problem also exists on other sites (for example udemy.com), but not all. After checking the common ground, I learned that all problematic sites are secured by Cloudflare. A internet research showed multiple results regarding Cloudflare blocking a whole IPv6 prefix. They were all created at the same time (seems to be one crosspost), but it describes exactly my problem: Cloudflare problems with IPv6 range visiting any website. Unfortunately, the comments don’t help me, ProjectHoneyPot doesn’t know any of my IPv6 addresses I used during my tests.
I also checked the network for any “bots” or similar, but everything looks okay.
I created an account and a ticket at Cloudflare but it seems that due to a high demand support tickets per mail are currently prioritized for paying customers and they told me to ask the community and include “problem accessing sites secured by Cloudflare with IPv6” in the details.
Do you know, if there is any possibility to check if my IPv6 Prefix is being blocked? Or do you have any other idea what could be the problem?