named-rrchecker(1)
syntax checker for individual DNS resource records
Description
NAMED-RRCHECKER
NAME
named-rrchecker - syntax checker for individual DNS resource records
SYNOPSIS
named-rrchecker [-h] [-o origin] [-p] [-u] [-C] [-T] [-P]
DESCRIPTION
named-rrchecker
reads a single DNS resource record (RR) from standard input
and checks whether it is syntactically correct.
The input format is a minimal subset of the DNS zone file
format. The
entire input must be:
CLASS TYPE RDATA
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Input must not start with an owner (domain) name |
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The CLASS field is mandatory (typically IN). |
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The TTL field must not be present. |
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RDATA format is specific to each RRTYPE. |
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Leading and trailing whitespace in each field is ignored. |
Format details can be found in RFC 1035 Section 5.1 under <rr> specification. RFC 3597 format is also accepted in any of the input fields. See Examples.
OPTIONS
-o origin
This option specifies the origin to be used when interpreting names in the record: it defaults to root (.). The specified origin is always taken as an absolute name.
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-p |
This option prints out the resulting record in canonical form. If there is no canonical form defined, the record is printed in RFC 3597 unknown record format. | ||
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-u |
This option prints out the resulting record in RFC 3597 unknown record format. |
-C, -T, -P
These options do not read input. They print out known classes, standard types, and private type mnemonics. Each item is printed on a separate line. The resulting list of private types may be empty
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-h |
This option prints out the help menu. |
EXAMPLES
Pay close
attention to the echo command line options -e
and -n, as they affect whitespace in the input to
named-rrchecker.
echo -n 'IN A 192.0.2.1' | named-rrchecker
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Valid input is in RFC 1035 format with no newline at the end of the input. | ||
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Return code 0. |
echo -e '\n \n IN\tA 192.0.2.1 \t \n\n ' | named-rrchecker -p
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Valid input with leading and trailing whitespace. |
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Output: IN A 192.0.2.1 |
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Leading and trailing whitespace is not part of the output. |
Relative names and origin
echo 'IN CNAME target' | named-rrchecker -p
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Valid input with a relative name as the CNAME target. | ||
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Output: IN CNAME target. | ||
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Relative name target from the input is converted to an absolute name using the default origin . (root). |
echo 'IN CNAME target' | named-rrchecker -p -o origin.test
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Valid input with a relative name as the CNAME target. | ||
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Output: IN CNAME target.origin.test. | ||
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Relative name target from the input is converted to an absolute name using the specified origin origin.test |
echo 'IN CNAME target.' | named-rrchecker -p -o origin.test
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Valid input with an absolute name as the CNAME target. | ||
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Output: IN CNAME target. | ||
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The specified origin has no influence if target from the input is already absolute. |
Special characters
Special
characters allowed in zone files by RFC 1035 Section
5.1 are accepted.
echo 'IN CNAME t\097r\get\.' | named-rrchecker -p -o
origin.test
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Valid input with backslash escapes. | ||
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Output: IN CNAME target\..origin.test. | ||
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\097 denotes an ASCII value in decimal, which, in this example, is the character a. | ||
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\g is converted to a plain g because the g character does not have a special meaning and so the \ prefix does nothing in this case. | ||
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\. denotes a literal ASCII dot (here as a part of the CNAME target name). Special meaning of . as the DNS label separator was disabled by the preceding \ prefix. |
echo 'IN CNAME @' | named-rrchecker -p -o origin.test
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Valid input with @ used as a reference to the specified origin. |
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Output: IN CNAME origin.test. |
echo 'IN CNAME \@' | named-rrchecker -p -o origin.test
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Valid input with a literal @ character (escaped). |
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Output: IN CNAME \@.origin.test. |
echo 'IN CNAME prefix.@' | named-rrchecker -p -o origin.test
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Valid input with @ used as a reference to the specifed origin. |
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Output: IN CNAME prefix.\@.origin.test. |
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@ has special meaning only if it is free-standing. |
echo 'IN A 192.0.2.1; comment' | named-rrchecker -p
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Valid input with a trailing comment. Note the lack of whitespace before the start of the comment. | ||
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Output: IN A 192.0.2.1 |
For multi-line examples see the next section.
Multi-token records
echo -e 'IN TXT two words \n' | named-rrchecker -p
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Valid TXT RR with two unquoted words and trailing whitespace. | ||
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Output: IN TXT "two" "words" | ||
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Two unquoted words in the input are treated as two <character-string>s per RFC 1035 Section 3.3.14. | ||
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Trailing whitespace is omitted from the last <character-string>. |
echo -e 'IN TXT "two words" \n' | named-rrchecker -p
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Valid TXT RR with one character-string and trailing whitespace. |
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Output: IN TXT "two words" |
echo -e 'IN TXT "problematic newline\n"' | named-rrchecker -p
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Invalid input - the closing " is not detected before the end of the line. |
echo 'IN TXT "with newline\010"' | named-rrchecker -p
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Valid input with an escaped newline character inside character-string. | ||
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Output: IN TXT "with newline\010" |
echo -e 'IN TXT ( two\nwords )' | named-rrchecker -p
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Valid multi-line input with line continuation allowed inside optional parentheses in the RDATA field. | ||
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Output: IN TXT "two" "words" |
echo -e 'IN TXT ( two\nwords ; misplaced comment )' | named-rrchecker -p
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Invalid input - comments, starting with ";", are ignored by the parser, so the closing parenthesis should be before the semicolon. |
echo -e 'IN TXT ( two\nwords ; a working comment\n )' | named-rrchecker -p
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Valid input - the comment is terminated with a newline. |
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Output: IN TXT "two" "words" |
echo 'IN HTTPS 1 . alpn="h2,h3"' | named-rrchecker -p
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Valid HTTPS record |
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Output: IN HTTPS 1 . alpn="h2,h3" |
echo -e 'IN HTTPS ( 1 \n . \n alpn="dot")port=853' | named-rrchecker -p
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Valid HTTPS record with individual sub-fields split across multiple lines using RFC 1035 Section 5.1 parentheses syntax to group data that crosses a line boundary. | ||
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Note the missing whitespace between the closing parenthesis and adjacent tokens. | ||
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Output: IN HTTPS 1 . alpn="dot" port=853 |
Unknown type handling
echo 'IN A 192.0.2.1' | named-rrchecker -u
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Valid input in RFC 1035 format. |
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Output in RFC 3957 format: CLASS1 TYPE1 \# 4 C0000201 |
echo 'CLASS1 TYPE1 \# 4 C0000201' | named-rrchecker -p
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Valid input in RFC 3597 format. |
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Output in RFC 1035 format: IN A 192.0.2.1 |
echo 'IN A \# 4 C0000201' | named-rrchecker -p
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Valid input with class and type in RFC 1035 format and rdata in - RFC 3597 format. | ||
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Output in RFC 1035 format: IN A 192.0.2.1 |
echo 'IN HTTPS 1 . key3=\001\000' | named-rrchecker -p
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Valid input with RFC 9460 syntax for an unknown key3 field. Syntax \001\000 produces two octets with values 1 and 0, respectively. | ||
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Output: IN HTTPS 1 . port=256 | ||
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key3 matches the standardized key name port. | ||
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Octets 1 and 0 were decoded as integer values in big-endian encoding. |
echo 'IN HTTPS 1 . key3=\001' | named-rrchecker -p
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Invalid input - the length of the value for key3 (i.e. port) does not match the known standard format for that parameter in the SVCB RRTYPE. |
echo 'IN HTTPS 1 . port=\001\000' | named-rrchecker -p
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Invalid input - the key port, when specified using its standard mnemonic name, must use standard key-specific syntax. |
Meta values
echo 'IN AXFR' | named-rrchecker
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Invalid input - AXFR is a meta type, not a genuine RRTYPE. |
echo 'ANY A 192.0.2.1' | named-rrchecker
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Invalid input - ANY is meta class, not a true class. |
echo 'A 192.0.2.1' | named-rrchecker
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Invalid input - the class field is missing, so the parser would try and fail to interpret the RRTYPE A as the class. |
RETURN CODES
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0 |
The whole input was parsed as one syntactically valid resource record. | ||
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1 |
The input is not a syntactically valid resource record, or the given type is not supported, or either/both class and type are meta-values, which should not appear in zone files. |
SEE ALSO
RFC 1034, RFC 1035, RFC 3957, named(8).
AUTHOR
Internet Systems Consortium
COPYRIGHT
2025, Internet Systems Consortium