dns/man/coredns-rewrite.7

.\" Generated by Mmark Markdown Processer - mmark.miek.nl
.TH "COREDNS-REWRITE" 7 "March 2026" "CoreDNS" "CoreDNS Plugins"

.SH "NAME"
.PP
\fIrewrite\fP - performs internal message rewriting.

.SH "DESCRIPTION"
.PP
Rewrites are invisible to the client. There are simple rewrites (fast) and complex rewrites
(slower), but they're powerful enough to accommodate most dynamic back-end applications.

.SH "SYNTAX"
.PP
A simplified/easy-to-digest syntax for \fIrewrite\fP is...

.PP
.RS

.nf
rewrite [continue|stop] FIELD [TYPE] [(FROM TO)|TTL] [OPTIONS]

.fi
.RE

.IP \(bu 4
\fBFIELD\fP indicates what part of the request/response is being re-written.

.RS
.IP \(en 4
\fB\fCtype\fR - the type field of the request will be rewritten. FROM/TO must be a DNS record type (\fB\fCA\fR, \fB\fCMX\fR, etc.);
e.g., to rewrite ANY queries to HINFO, use \fB\fCrewrite type ANY HINFO\fR.
.IP \(en 4
\fB\fCname\fR - the query name in the \fIrequest\fP is rewritten; by default this is a full match of the
name, e.g., \fB\fCrewrite name example.net example.org\fR. Other match types are supported, see the \fBName Field Rewrites\fP section below.
.IP \(en 4
\fB\fCclass\fR - the class of the message will be rewritten. FROM/TO must be a DNS class type (\fB\fCIN\fR, \fB\fCCH\fR, or \fB\fCHS\fR); e.g., to rewrite CH queries to IN use \fB\fCrewrite class CH IN\fR.
.IP \(en 4
\fB\fCedns0\fR - an EDNS0 option can be appended to the request as described below in the \fBEDNS0 Options\fP section.
.IP \(en 4
\fB\fCttl\fR - the TTL value in the \fIresponse\fP is rewritten.
.IP \(en 4
\fB\fCcname\fR - the CNAME target if the response has a CNAME record
.IP \(en 4
\fB\fCrcode\fR - the response code (RCODE) value in the \fIresponse\fP is rewritten.

.RE
.IP \(bu 4
\fBTYPE\fP this optional element can be specified for a \fB\fCname\fR or \fB\fCttl\fR field.
If not given type \fB\fCexact\fR will be assumed. If options should be specified the
type must be given.
.IP \(bu 4
\fBFROM\fP is the name (exact, suffix, prefix, substring, or regex) or type to match
.IP \(bu 4
\fBTO\fP is the destination name or type to rewrite to
.IP \(bu 4
\fBTTL\fP is the number of seconds to set the TTL value to (only for field \fB\fCttl\fR)
.IP \(bu 4
\fBOPTIONS\fP


.PP
for field \fB\fCname\fR further options are possible controlling the response rewrites.
  All name matching types support the following options

.PP
.RS

.nf
 * `answer auto` \- the names in the \_response\_ is rewritten in a best effort manner.
 * `answer name FROM TO` \- the query name in the \_response\_ is rewritten matching the from regex pattern.
 * `answer value FROM TO` \- the names in the \_response\_ is rewritten matching the from regex pattern.

.fi
.RE

.PP
See below in the \fBResponse Rewrites\fP section for further details.

.PP
If you specify multiple rules and an incoming query matches multiple rules, the rewrite
will behave as follows:

.IP \(bu 4
\fB\fCcontinue\fR will continue applying the next rule in the rule list.
.IP \(bu 4
\fB\fCstop\fR will consider the current rule the last rule and will not continue.  The default behaviour is \fB\fCstop\fR
.IP \(bu 4
When multiple rules are matched, the request rewrite follows the line order in the configuration, while the response rewrite(\fB\fCanswer\fR option) is executed in reverse order.


.SH "EXAMPLES"
.SS "NAME FIELD REWRITES"
.PP
The \fB\fCrewrite\fR plugin offers the ability to match the name in the question section of
a DNS request. The match could be exact, a substring match, or based on a prefix, suffix, or regular
expression. If the newly used name is not a legal domain name, the plugin returns an error to the
client.

.PP
The syntax for name rewriting is as follows:

.PP
.RS

.nf
rewrite [continue|stop] name [exact|prefix|suffix|substring|regex] STRING STRING [OPTIONS]

.fi
.RE

.PP
The match type, e.g., \fB\fCexact\fR, \fB\fCsubstring\fR, etc., triggers rewrite:

.IP \(bu 4
\fBexact\fP (default): on an exact match of the name in the question section of a request
.IP \(bu 4
\fBsubstring\fP: on a partial match of the name in the question section of a request
.IP \(bu 4
\fBprefix\fP: when the name begins with the matching string
.IP \(bu 4
\fBsuffix\fP: when the name ends with the matching string
.IP \(bu 4
\fBregex\fP: when the name in the question section of a request matches a regular expression.
Regex patterns must not exceed 10000 characters.


.PP
If the match type is omitted, the \fB\fCexact\fR match type is assumed. If OPTIONS are
given, the type must be specified.

.PP
The following instruction allows rewriting names in the query that
contain the substring \fB\fCservice.us-west-1.example.org\fR:

.PP
.RS

.nf
rewrite name substring service.us\-west\-1.example.org service.us\-west\-1.consul

.fi
.RE

.PP
Thus:

.IP \(bu 4
Incoming Request Name: \fB\fCftp.service.us-west-1.example.org\fR
.IP \(bu 4
Rewritten Request Name: \fB\fCftp.service.us-west-1.consul\fR


.PP
The following instruction uses regular expressions. Names in requests
matching the regular expression \fB\fC(.*)-(us-west-1)\.example\.org\fR are replaced with
\fB\fC{1}.service.{2}.consul\fR, where \fB\fC{1}\fR and \fB\fC{2}\fR are regular expression match groups.

.PP
.RS

.nf
rewrite name regex (.*)\-(us\-west\-1)\\.example\\.org {1}.service.{2}.consul

.fi
.RE

.PP
Thus:

.IP \(bu 4
Incoming Request Name: \fB\fCftp-us-west-1.example.org\fR
.IP \(bu 4
Rewritten Request Name: \fB\fCftp.service.us-west-1.consul\fR


.PP
The following example rewrites the \fB\fCschmoogle.com\fR suffix to \fB\fCgoogle.com\fR.

.PP
.RS

.nf
rewrite name suffix .schmoogle.com. .google.com.

.fi
.RE

.SS "RESPONSE REWRITES"
.PP
When rewriting incoming DNS requests' names (field \fB\fCname\fR), CoreDNS re-writes
the \fB\fCQUESTION SECTION\fR
section of the requests. It may be necessary to rewrite the \fB\fCANSWER SECTION\fR of the
requests, because some DNS resolvers treat mismatches between the \fB\fCQUESTION SECTION\fR
and \fB\fCANSWER SECTION\fR as a man-in-the-middle attack (MITM).

.PP
For example, a user tries to resolve \fB\fCftp-us-west-1.coredns.rocks\fR. The
CoreDNS configuration file has the following rule:

.PP
.RS

.nf
rewrite name regex (.*)\-(us\-west\-1)\\.coredns\\.rocks {1}.service.{2}.consul

.fi
.RE

.PP
CoreDNS rewrote the request from \fB\fCftp-us-west-1.coredns.rocks\fR to
\fB\fCftp.service.us-west-1.consul\fR and ultimately resolved it to 3 records.
The resolved records, in the \fB\fCANSWER SECTION\fR below, were not from \fB\fCcoredns.rocks\fR, but
rather from \fB\fCservice.us-west-1.consul\fR.

.PP
.RS

.nf
$ dig @10.1.1.1 ftp\-us\-west\-1.coredns.rocks

;; QUESTION SECTION:
;ftp\-us\-west\-1.coredns.rocks. IN A

;; ANSWER SECTION:
ftp.service.us\-west\-1.consul. 0    IN A    10.10.10.10
ftp.service.us\-west\-1.consul. 0    IN A    10.20.20.20
ftp.service.us\-west\-1.consul. 0    IN A    10.30.30.30

.fi
.RE

.PP
The above is a mismatch between the question asked and the answer provided.

.PP
There are three possibilities to specify an answer rewrite:
- A rewrite can request a best effort answer rewrite by adding the option \fB\fCanswer auto\fR.
- A rewrite may specify a dedicated regex based response name rewrite with the
  \fB\fCanswer name FROM TO\fR option.
- A regex based rewrite of record values like \fB\fCCNAME\fR, \fB\fCSRV\fR, etc, can be requested by
  an \fB\fCanswer value FROM TO\fR option.

.PP
Hereby FROM/TO follow the rules for the \fB\fCregex\fR name rewrite syntax.

.SS "AUTO RESPONSE NAME REWRITE"
.PP
The following configuration snippet allows for rewriting of the
\fB\fCANSWER SECTION\fR according to the rewrite of the \fB\fCQUESTION SECTION\fR:

.PP
.RS

.nf
    rewrite stop {
        name suffix .coredns.rocks .service.consul answer auto
    }

.fi
.RE

.PP
Any occurrence of the rewritten question in the answer is mapped
back to the original value before the rewrite.

.PP
Please note that answers for rewrites of type \fB\fCexact\fR are always rewritten.
For a \fB\fCsuffix\fR name rule \fB\fCauto\fR leads to a reverse suffix response rewrite,
exchanging FROM and TO from the rewrite request.

.SS "EXPLICIT RESPONSE NAME REWRITE"
.PP
The following configuration snippet allows for rewriting of the
\fB\fCANSWER SECTION\fR, provided that the \fB\fCQUESTION SECTION\fR was rewritten:

.PP
.RS

.nf
    rewrite stop {
        name regex (.*)\-(us\-west\-1)\\.coredns\\.rocks {1}.service.{2}.consul
        answer name (.*)\\.service\\.(us\-west\-1)\\.consul {1}\-{2}.coredns.rocks
    }

.fi
.RE

.PP
Now, the \fB\fCANSWER SECTION\fR matches the \fB\fCQUESTION SECTION\fR:

.PP
.RS

.nf
$ dig @10.1.1.1 ftp\-us\-west\-1.coredns.rocks

;; QUESTION SECTION:
;ftp\-us\-west\-1.coredns.rocks. IN A

;; ANSWER SECTION:
ftp\-us\-west\-1.coredns.rocks. 0    IN A    10.10.10.10
ftp\-us\-west\-1.coredns.rocks. 0    IN A    10.20.20.20
ftp\-us\-west\-1.coredns.rocks. 0    IN A    10.30.30.30

.fi
.RE

.SS "REWRITING OTHER RESPONSE VALUES"
.PP
It is also possible to rewrite other values returned in the DNS response records
(e.g. the server names returned in \fB\fCSRV\fR and \fB\fCMX\fR records). This can be enabled by adding
the \fB\fCanswer value FROM TO\fR option to a name rule as specified below. \fB\fCanswer value\fR takes a
regular expression and a rewrite name as parameters and works in the same way as the
\fB\fCanswer name\fR rule.

.PP
Note that names in the \fB\fCAUTHORITY SECTION\fR and \fB\fCADDITIONAL SECTION\fR will also be
rewritten following the specified rules. The names returned by the following
record types: \fB\fCCNAME\fR, \fB\fCDNAME\fR, \fB\fCSOA\fR, \fB\fCSRV\fR, \fB\fCMX\fR, \fB\fCNAPTR\fR, \fB\fCNS\fR, \fB\fCPTR\fR will be rewritten
if the \fB\fCanswer value\fR rule is specified.

.PP
The syntax for the rewrite of DNS request and response is as follows:

.PP
.RS

.nf
rewrite [continue|stop] {
    name regex STRING STRING
    answer name STRING STRING
    [answer value STRING STRING]
}

.fi
.RE

.PP
Note that the above syntax is strict.  For response rewrites, only \fB\fCname\fR
rules are allowed to match the question section. The answer rewrite must be
after the name, as in the syntax example.

.SS "EXAMPLE: PTR RESPONSE VALUE REWRITE"
.PP
The original response contains the domain \fB\fCservice.consul.\fR in the \fB\fCVALUE\fR part
of the \fB\fCANSWER SECTION\fR

.PP
.RS

.nf
$ dig @10.1.1.1 30.30.30.10.in\-addr.arpa PTR

;; QUESTION SECTION:
;30.30.30.10.in\-addr.arpa. IN PTR

;; ANSWER SECTION:
30.30.30.10.in\-addr.arpa. 60    IN PTR    ftp\-us\-west\-1.service.consul.

.fi
.RE

.PP
The following configuration snippet allows for rewriting of the value
in the \fB\fCANSWER SECTION\fR:

.PP
.RS

.nf
    rewrite stop {
        name suffix .arpa .arpa
        answer name auto
        answer value (.*)\\.service\\.consul\\. {1}.coredns.rocks.
    }

.fi
.RE

.PP
Now, the \fB\fCVALUE\fR in the \fB\fCANSWER SECTION\fR has been overwritten in the domain part:

.PP
.RS

.nf
$ dig @10.1.1.1 30.30.30.10.in\-addr.arpa PTR

;; QUESTION SECTION:
;30.30.30.10.in\-addr.arpa. IN PTR

;; ANSWER SECTION:
30.30.30.10.in\-addr.arpa. 60    IN PTR    ftp\-us\-west\-1.coredns.rocks.

.fi
.RE

.SS "MULTIPLE RESPONSE REWRITES"
.PP
\fB\fCname\fR and \fB\fCvalue\fR rewrites can be chained by appending multiple answer rewrite
options. For all occurrences but the first one the keyword \fB\fCanswer\fR might be
omitted.

.PP
.RS

.nf
answer (auto | (name|value FROM TO)) { [answer] (auto | (name|value FROM TO)) }

.fi
.RE

.PP
For example:

.PP
.RS

.nf
rewrite [continue|stop] name regex FROM TO answer name FROM TO [answer] value FROM TO

.fi
.RE

.PP
When using \fB\fCexact\fR name rewrite rules, the answer gets rewritten automatically,
and there is no need to define \fB\fCanswer name auto\fR. But it is still possible to define
additional \fB\fCanswer value\fR and \fB\fCanswer value\fR options.

.PP
The rule below rewrites the name in a request from \fB\fCRED\fR to \fB\fCBLUE\fR, and subsequently
rewrites the name in a corresponding response from \fB\fCBLUE\fR to \fB\fCRED\fR. The
client in the request would see only \fB\fCRED\fR and no \fB\fCBLUE\fR.

.PP
.RS

.nf
rewrite [continue|stop] name exact RED BLUE

.fi
.RE

.SS "TTL FIELD REWRITES"
.PP
At times, the need to rewrite a TTL value could arise. For example, a DNS server
may not cache records with a TTL of zero (\fB\fC0\fR). An administrator
may want to increase the TTL to ensure it is cached, e.g., by increasing it to 15 seconds.

.PP
In the below example, the TTL in the answers for \fB\fCcoredns.rocks\fR domain are
being set to \fB\fC15\fR:

.PP
.RS

.nf
    rewrite continue {
        ttl regex (.*)\\.coredns\\.rocks 15
    }

.fi
.RE

.PP
By the same token, an administrator may use this feature to prevent or limit caching by
setting the TTL value really low.

.PP
The syntax for the TTL rewrite rule is as follows. The meaning of
\fB\fCexact|prefix|suffix|substring|regex\fR is the same as with the name rewrite rules.
An omitted type is defaulted to \fB\fCexact\fR.

.PP
.RS

.nf
rewrite [continue|stop] ttl [exact|prefix|suffix|substring|regex] STRING [SECONDS|MIN\-MAX]

.fi
.RE

.PP
It is possible to supply a range of TTL values in the \fB\fCSECONDS\fR parameters instead of a single value.
If a range is supplied, the TTL value is set to \fB\fCMIN\fR if it is below, or set to \fB\fCMAX\fR if it is above.
The TTL value is left unchanged if it is already inside the provided range.
The ranges can be unbounded on either side.

.PP
TTL examples with ranges:

.PP
.RS

.nf
rewrite ttl example.com. 30\-300

rewrite ttl example.com. \-30 # equivalent to rewrite ttl example.com. 0\-30

rewrite ttl example.com. 30\-

rewrite ttl example.com. 30 # equivalent to rewrite ttl example.com. 30\-30

.fi
.RE

.SS "RCODE FIELD REWRITES"
.PP
At times, the need to rewrite a RCODE value could arise. For example, a DNS server
may respond with a SERVFAIL instead of NOERROR records when AAAA records are requested.

.PP
In the below example, the rcode value the answer for \fB\fCcoredns.rocks\fR the replies with SERVFAIL
is being switched to NOERROR.

.PP
This example rewrites all the *.coredns.rocks domain SERVFAIL errors to NOERROR

.PP
.RS

.nf
    rewrite continue {
        rcode regex (.*)\\.coredns\\.rocks SERVFAIL NOERROR
    }

.fi
.RE

.PP
The same result numeric values:

.PP
.RS

.nf
    rewrite continue {
        rcode regex (.*)\\.coredns\\.rocks 2 0
    }

.fi
.RE

.PP
The syntax for the RCODE rewrite rule is as follows. The meaning of
\fB\fCexact|prefix|suffix|substring|regex\fR is the same as with the name rewrite rules.
An omitted type is defaulted to \fB\fCexact\fR.

.PP
.RS

.nf
rewrite [continue|stop] rcode [exact|prefix|suffix|substring|regex] STRING FROM TO

.fi
.RE

.PP
The values of FROM and TO can be any of the following, text value or numeric:

.PP
.RS

.nf
  0 NOERROR
  1 FORMERR
  2 SERVFAIL
  3 NXDOMAIN
  4 NOTIMP
  5 REFUSED
  6 YXDOMAIN
  7 YXRRSET
  8 NXRRSET
  9 NOTAUTH
  10 NOTZONE
  16 BADSIG
  17 BADKEY
  18 BADTIME
  19 BADMODE
  20 BADNAME
  21 BADALG
  22 BADTRUNC
  23 BADCOOKIE

.fi
.RE

.SH "EDNS0 OPTIONS"
.PP
Using the FIELD edns0, you can set, append, replace, or unset specific EDNS0 options in the request.

.IP \(bu 4
\fB\fCreplace\fR will modify any "matching" option with the specified option. The criteria for "matching" varies based on EDNS0 type.
.IP \(bu 4
\fB\fCappend\fR will add the option only if no matching option exists
.IP \(bu 4
\fB\fCset\fR will modify a matching option or add one if none is found
.IP \(bu 4
\fB\fCunset\fR will remove the matching option if one exists


.PP
Currently supported are \fB\fCEDNS0_LOCAL\fR, \fB\fCEDNS0_NSID\fR and \fB\fCEDNS0_SUBNET\fR.

.SS "EDNS0_LOCAL"
.PP
This has two fields, code and data. A match is defined as having the same code. Data may be a string or a variable.

.IP \(bu 4
A string data is treated as hex if it starts with \fB\fC0x\fR. Example:


.PP
.RS

.nf
\&. {
    rewrite edns0 local set 0xffee 0x61626364
    whoami
}

.fi
.RE

.PP
rewrites the first local option with code 0xffee, setting the data to "abcd". This is equivalent to:

.PP
.RS

.nf
\&. {
    rewrite edns0 local set 0xffee abcd
}

.fi
.RE

.IP \(bu 4
A variable data is specified with a pair of curly brackets \fB\fC{}\fR. Following are the supported variables:
{qname}, {qtype}, {client\fIip}, {client\fPport}, {protocol}, {server\fIip}, {server\fPport}.
.IP \(bu 4
If the metadata plugin is enabled, then labels are supported as variables if they are presented within curly brackets.
The variable data will be replaced with the value associated with that label. If that label is not provided,
the variable will be silently substituted with an empty string.


.PP
Examples:

.PP
.RS

.nf
rewrite edns0 local set 0xffee {client\_ip}

.fi
.RE

.PP
The following example uses metadata and an imaginary "some-plugin" that would provide "some-label" as metadata information.

.PP
.RS

.nf
metadata
some\-plugin
rewrite edns0 local set 0xffee {some\-plugin/some\-label}

.fi
.RE

.PP
A local option may be removed by unsetting its code. Example:

.PP
.RS

.nf
rewrite edns0 local unset 0xffee

.fi
.RE

.SS "EDNS0_NSID"
.PP
This has no fields; it will add an NSID option with an empty string for the NSID. If the option already exists
and the action is \fB\fCreplace\fR or \fB\fCset\fR, then the NSID in the option will be set to the empty string.
The option can be removed with the \fB\fCunset\fR action.

.SS "EDNS0_SUBNET"
.PP
This has two fields,  IPv4 bitmask length and IPv6 bitmask length. The bitmask
length is used to extract the client subnet from the source IP address in the query.

.PP
Example:

.PP
.RS

.nf
rewrite edns0 subnet set 24 56

.fi
.RE

.IP \(bu 4
If the query's source IP address is an IPv4 address, the first 24 bits in the IP will be the network subnet.
.IP \(bu 4
If the query's source IP address is an IPv6 address, the first 56 bits in the IP will be the network subnet.


.PP
This option can be removed by using \fB\fCunset\fR:

.PP
.RS

.nf
rewrite edns0 subnet unset

.fi
.RE

.SS "EDNS0 REVERT"
.PP
Using the \fB\fCrevert\fR flag, you can revert the changes made by this rewrite call, so the response will not contain this option.

.PP
This example sets option, but response will not contain it

.PP
.RS

.nf
\&. {
    rewrite edns0 local set 0xffee abcd revert
}

.fi
.RE

.PP
If only some calls contain the \fB\fCrevert\fR flag, then the value in the response will be changed to the previous one. So, in this example, the response will contain \fB\fCabcd\fR data at \fB\fC0xffee\fR

.PP
.RS

.nf
\&. {
    rewrite continue {
        edns0 local set 0xffee abcd
    }
    
    rewrite edns0 local replace 0xffee bcde revert
}

.fi
.RE

.SH "CNAME FIELD REWRITES"
.PP
There might be a scenario where you want the \fB\fCCNAME\fR target of the response to be rewritten. You can do this by using the \fB\fCCNAME\fR field rewrite. Answer records preceding the \fB\fCCNAME\fR target are kept unchanged, the \fB\fCCNAME\fR target is rewritten, and the subsequent records are replaced with the lookup result of the rewritten \fB\fCCNAME\fR target.

.PP
The syntax for the \fB\fCCNAME\fR rewrite rule is as follows. The meaning of
\fB\fCexact|prefix|suffix|substring|regex\fR is the same as with the name rewrite rules.
An omitted type is defaulted to \fB\fCexact\fR.

.PP
.RS

.nf
rewrite [continue|stop] cname [exact|prefix|suffix|substring|regex] FROM TO

.fi
.RE

.PP
Consider the following \fB\fCCNAME\fR rewrite rule with regex type.

.PP
.RS

.nf
rewrite cname regex (.*).cdn.example.net. {1}.other.cdn.com.

.fi
.RE

.PP
If you were to send the following DNS request without the above rule, an example response would be:

.PP
.RS

.nf
$ dig @10.1.1.1 my\-app.com

;; QUESTION SECTION:
;my\-app.com. IN A

;; ANSWER SECTION:
my\-app.com.                  200  IN  CNAME  my\-app.example.
my\-app.example.              200  IN  CNAME  my\-app.com.cdn.example.net.
my\-app.com.cdn.example.net.  300  IN  A      20.2.0.1
my\-app.com.cdn.example.net.  300  IN  A      20.2.0.2

.fi
.RE

.PP
If you were to send the same DNS request with the above rule set up, an example response would be:

.PP
.RS

.nf
$ dig @10.1.1.1 my\-app.com

;; QUESTION SECTION:
;my\-app.com. IN A

;; ANSWER SECTION:
my\-app.com.                  200  IN  CNAME  my\-app.example.
my\-app.example.              200  IN  CNAME  my\-app.com.other.cdn.com.
my\-app.com.other.cdn.com.    100  IN  A      30.3.1.2

.fi
.RE

.PP
Note that the answer will contain a completely different set of answer records after rewriting the \fB\fCCNAME\fR target.