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Unable to create A DNS record with underscore in Plesk: The specified domain name is not valid. You need to specify a valid domain name like domain.com.

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Kuzma Ivanov
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Plesk for Windows Plesk for Linux kb: technical

Applicable to:

  • Plesk for Linux
  • Plesk for Windows

Symptoms

When adding an A record that includes an underscore symbol '_' in Plesk at Domains > example.com > Hosting & DNS > DNS Settings, the following message appears:

PLESK_ERROR: The specified domain name is not valid. You need to specify a valid domain name like domain.com.

Cause

Underscore characters are not permitted in domain names according to RFC 1035. Only letters, digits, and hyphens are allowed. Even though some DNS servers allow the use of underscores (e.g. Windows DNS Manager) with the records below, such configuration is not possible:

NS / A / AAAA / MX / AXFR / CAA

Resolution

Underscores can be used with CNAME, SRV, TXT, DS records.

As a workaround, create a CNAME record instead of an A record.

Comments

1 comment

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  • Avatar
    Carl Swart

    RFC 1035 is superseded by the amendments of RFC 2181. RFC2181 states:

       Similarly, any binary string can serve as the value
   of any record that includes a domain name as some or all of its value
   (SOA, NS, MX, PTR, CNAME, and any others that may be added).
   Implementations of the DNS protocols must not place any restrictions
   on the labels that can be used.  In particular, DNS servers must not
   refuse to serve a zone because it contains labels that might not be
   acceptable to some DNS client programs.

    So, the limit on NS and MX records as explained in this support article, does not make sense. Then again, I am no RFC expert and may simply have a fundamental misunderstanding of how RFCs work.

    The definitive descriptions of the rules for forming domain names appear in RFC 1035, RFC 1123, RFC 2181, and RFC 5892. A domain name consists of one or more parts, technically called labels, that are conventionally concatenated, and delimited by dots, such as example.com.

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