nat64ptr

coredns-nat64ptr-plugin

coredns-nat64ptr-plugin is a CoreDNS plugin named nat64ptr. It rewrites PTR lookups under a configured NAT64 /96 IPv6 reverse zone into the embedded IPv4 address's in-addr.arpa. PTR lookup, forwards the request to the next plugin, then rewrites response owner names back to the original ip6.arpa. name.

This is useful when IPv6-only clients behind NAT64 need reverse DNS for IPv4 destinations represented inside a NAT64 prefix.

Project Name

• Project/module name: coredns-nat64ptr-plugin
• CoreDNS plugin directive: nat64ptr
• Go module path: github.com/sunoaki/coredns-nat64ptr-plugin

Corefile

. {
    nat64ptr 2602:2a3:4:9b64:2::/96
    forward . 172.16.0.53
}

Only PTR questions below the configured /96 reverse zone are handled. Other requests are passed to the next plugin unchanged. A second optional argument configures the backend reverse suffix; it defaults to in-addr.arpa.. A third optional argument appends a suffix to returned PTR targets.

nat64ptr 2602:2a3:4:9b64:2::/96 in-addr.arpa.

nat64ptr 2602:2a3:4:9b64:2::/96 in-addr.arpa. 42xlat.sunoaki.net

Query Flow

For 2602:2a3:4:9b64:2::172.23.0.53, the IPv6 reverse name starts with the embedded IPv4 nibbles:

5.3.0.0.7.1.c.a...

nat64ptr converts those nibbles into 53.0.23.172.in-addr.arpa., forwards the rewritten request to the next plugin, then rewrites the response Question and Answer owner names back to the original IPv6 ip6.arpa. name. If a PTR suffix is configured, a returned target such as burble.dn42. becomes burble.dn42.42xlat.sunoaki.net..

CoreDNS Integration

Add this plugin to CoreDNS plugin.cfg before the plugin that should receive the rewritten IPv4 PTR query, usually before forward:

nat64ptr:github.com/sunoaki/coredns-nat64ptr-plugin

Then rebuild CoreDNS with the normal CoreDNS build process.

Development

Run the unit tests with:

go test ./...

Files

• setup.go: CoreDNS registration and Corefile parsing.
• nat64ptr.go: PTR request matching, IPv4 extraction, downstream forwarding, and response rewriting.
• nat64ptr_test.go: Unit tests for extraction and end-to-end rewrite behavior.