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* doc update Go through all README and fix mistakes, extend example and let more corefile snippets be test for validity. * Cant use spefic addr in test
99 lines
3.1 KiB
Markdown
99 lines
3.1 KiB
Markdown
# rewrite
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*rewrite* performs internal message rewriting.
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Rewrites are invisible to the client. There are simple rewrites (fast) and complex rewrites
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(slower), but they're powerful enough to accommodate most dynamic back-end applications.
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## Syntax
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~~~
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rewrite [continue|stop] FIELD FROM TO
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~~~
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* **FIELD** is (`type`, `class`, `name`, ...)
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* **FROM** is the exact name of type to match
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* **TO** is the destination name or type to rewrite to
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When the FIELD is `type` and FROM is (`A`, `MX`, etc.), the type of the message will be rewritten;
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e.g., to rewrite ANY queries to HINFO, use `rewrite type ANY HINFO`.
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When the FIELD is `class` and FROM is (`IN`, `CH`, or `HS`) the class of the message will be
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rewritten; e.g., to rewrite CH queries to IN use `rewrite class CH IN`.
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When the FIELD is `name` the query name in the message is rewritten; this
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needs to be a full match of the name, e.g., `rewrite name miek.nl example.org`.
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When the FIELD is `edns0` an EDNS0 option can be appended to the request as described below.
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If you specify multiple rules and an incoming query matches on multiple rules, the rewrite
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will behave as following
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* `continue` will continue apply the next rule in the rule list.
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* `stop` will consider the current rule is the last rule and will not continue. Default behaviour
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for not specifying this rule processing mode is `stop`
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## EDNS0 Options
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Using FIELD edns0, you can set, append, or replace specific EDNS0 options on the request.
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* `replace` will modify any matching (what that means may vary based on EDNS0 type) option with the specified option
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* `append` will add the option regardless of what options already exist
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* `set` will modify a matching option or add one if none is found
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Currently supported are `EDNS0_LOCAL`, `EDNS0_NSID` and `EDNS0_SUBNET`.
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### `EDNS0_LOCAL`
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This has two fields, code and data. A match is defined as having the same code. Data may be a string or a variable.
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* A string data can be treated as hex if it starts with `0x`. Example:
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~~~ corefile
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. {
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rewrite edns0 local set 0xffee 0x61626364
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whoami
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}
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~~~
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rewrites the first local option with code 0xffee, setting the data to "abcd". Equivalent:
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~~~ corefile
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. {
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rewrite edns0 local set 0xffee abcd
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}
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~~~
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* A variable data is specified with a pair of curly brackets `{}`. Following are the supported variables:
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* {qname}
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* {qtype}
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* {client_ip}
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* {client_port}
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* {protocol}
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* {server_ip}
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* {server_port}
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Example:
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~~~
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rewrite edns0 local set 0xffee {client_ip}
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~~~
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### `EDNS0_NSID`
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This has no fields; it will add an NSID option with an empty string for the NSID. If the option already exists
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and the action is `replace` or `set`, then the NSID in the option will be set to the empty string.
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### `EDNS0_SUBNET`
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This has two fields, IPv4 bitmask length and IPv6 bitmask length. The bitmask
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length is used to extract the client subnet from the source IP address in the query.
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Example:
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~~~
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rewrite edns0 subnet set 24 56
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~~~
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* If the query has source IP as IPv4, the first 24 bits in the IP will be the network subnet.
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* If the query has source IP as IPv6, the first 56 bits in the IP will be the network subnet.
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