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Can IPv6 and IPv4 work simultaneously?

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up vote 5 down vote accepted

It depends in what context you're referring to.

  • If you're asking whether a given NIC on a given OS can have both an IPv4 and IPv6 address at the same time, yes. This is more "coexisting" than "using simultaneously". Think of them as parallel network stacks -- network traffic will use one or the other but not both.

  • If you're asking whether a given application can access a network resource with both at the same time, kinda-sorta-maybe-ish. There are methods to allow interoperability and communication between the two, but they are 2 completely separate protocols.

This great article "Interoperability between IPv6 and IPv4" covers it pretty well. The site appears to be down hence the cache link.

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The site works fine for me when I allow HTTP access through my IP blockers. – Synetech Dec 9 '09 at 22:19
firefox is at least supposed to be able to browse v6 only sites and v4 only sites. It tries DNS lookups for v4 and v6 (A and AAAA) in parallel, and then decides which one to use. – Peter Cordes Dec 10 '09 at 4:09

IPv6 and v4 can "work simultaneously" through the use of tunneling. The wikipedia page here talks about it. I also suggest you read their page on IPv6 transitioning here they go into more specific descriptions on how they use tunneling for ipv6

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