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56 lines
2.1 KiB
Markdown
56 lines
2.1 KiB
Markdown
---
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name: REV
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parameters:
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- address
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parameter_types:
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address: string
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ts_return: string
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---
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`REV` returns the reverse lookup domain for an IP network. For
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example `REV('1.2.3.0/24')` returns `3.2.1.in-addr.arpa.` and
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`REV('2001:db8:302::/48)` returns `2.0.3.0.8.b.d.0.1.0.0.2.ip6.arpa.`.
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This is used in [`D()`](D.md) functions to create reverse DNS lookup zones.
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This is a convenience function. You could specify `D("3.2.1.in-addr.arpa",
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...` if you like to do things manually but why would you risk making
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typos?
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`REV` complies with RFC2317, "Classless in-addr.arpa delegation"
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for netmasks of size /25 through /31.
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While the RFC permits any format, we abide by the recommended format:
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`FIRST/MASK.C.B.A.in-addr.arpa` where `FIRST` is the first IP address
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of the zone, `MASK` is the netmask of the zone (25-31 inclusive),
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and A, B, C are the first 3 octets of the IP address. For example
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`172.20.18.130/27` is located in a zone named
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`128/27.18.20.172.in-addr.arpa`
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If the address does not include a "/" then `REV` assumes /32 for IPv4 addresses
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and /128 for IPv6 addresses.
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Note that the lower bits (the ones outside the netmask) must be zeros. They are not
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zeroed out automatically. Thus, `REV("1.2.3.4/24")` is an error. This is done
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to catch typos.
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{% code title="dnsconfig.js" %}
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```javascript
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D(REV("1.2.3.0/24"), REGISTRAR, DnsProvider(BIND),
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PTR("1", "foo.example.com."),
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PTR("2", "bar.example.com."),
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PTR("3", "baz.example.com."),
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// These take advantage of DNSControl's ability to generate the right name:
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PTR("1.2.3.10", "ten.example.com."),
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);
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D(REV("2001:db8:302::/48"), REGISTRAR, DnsProvider(BIND),
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PTR("1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0", "foo.example.com."), // 2001:db8:302::1
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// These take advantage of DNSControl's ability to generate the right name:
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PTR("2001:db8:302::2", "two.example.com."), // 2.0.0...
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PTR("2001:db8:302::3", "three.example.com."), // 3.0.0...
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);
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```
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{% endcode %}
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In the future we plan on adding a flag to [`A()`](../domain/A.md)which will insert
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the correct PTR() record in the appropriate `D(REV())` domain (i.e. `.arpa` domain) has been
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defined.
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