May 2011
Intermediate to advanced
52 pages
1h 5m
English
Content preview from DNS and BIND on IPv6Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapter 4. DNS64
During the (likely very long) transition from IPv4 to IPv6, ISPs and other organizations will implement new networks that only support IPv6. For the foreseeable future, though, clients on those networks will still need access to services (e.g., websites) that don’t yet support IPv6. NAT64 and DNS64[3] are a pair of complementary transition technologies that help provide that access.
NAT64 is a function run on a dual-stack host. A NAT64 server accepts connections from clients that only speak IPv6 and then uses its own IPv4 connectivity to communicate with IPv4-only servers on those clients’ behalf, then copies data between the IPv4 and IPv6 connections, effectively “bridging” the IPv4 and IPv6 networks. The clients don’t actually realize they’re connecting through NAT64—they’re led to believe that the IPv4-only servers they want to communicate with support IPv6 and that they’re talking directly to them.
How is that misdirection achieved? Through DNS—DNS64, in particular. The IPv6-only clients are configured to use one or more special name servers that support the DNS64 function. When one of these name servers receives a query from a client for AAAA (IPv6 address) records for some domain name, it looks for an answer, as it normally would. If it doesn’t find any such records, it tries looking up A records for the same domain name. If it finds one or more A records, it doesn’t return them to the client (which can’t use them, anyway, and wouldn’t accept them, since it ...
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