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I would not recommend IP based redirects. You can detect and do an initial redirect (with a javascript overlay telling people that you think they are in a specific area), but you'd have to give all users (including Googlebot) the ability to go to the other URLs as well. HREFLANG is not meant for geo-targeting and IP addresses only tell you location. You only need HREFLANG if there are language changes within a country targeted site or universal (not geotargeted) site. Even ignoring that, the HREFLANG would not help if people were always redirected based on IP, so I don't suggest that. Hope this helps, let me know if you have any more questions.