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Jordan Reiter
Asked: 2015-01-27 06:59:06 +0800 CST

Are there cases where the value for REMOTE_ADDR will be IPv6?

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Even with fairly widespread acceptance/implementation/adoption of IPv6, I have only ever seen IPv4 addresses used for the REMOTE_ADDR value.

Assuming I am using the REMOTE_ADDR for things like allowing access, is it realistic to expect and accept IPv4 addresses only, at least for the foreseeable future?

web-server

1 Answers

  1. If your server only has IPv4 then IPv6 users will be unable to connect to it. IPv4 users and users who have both IPv4 and IPv6 will connect using IPv4, so you'll only see IPv4 addresses in REMOTE_ADDR until you make your server accessible over IPv6. Which is something you should do as the number of users with IPv6 connectivity is growing fast.

    One thing that worries me about your question is that you mention using REMOTE_ADDR for access control and things like that. I hope you realise that you cannot assume that each user had a different IP address. IP addresses are shared amongst users with NAT. Because of the shortage of IPv4 addresses more and more ISPs need to share addresses between large groups of customers. Things like access control and rate limiting by IP address are already unreliable and will become unusable in the near future.

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