Rules for an FQDN for SSL/TLS certificates

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Rules for an FQDN for SSL/TLS certificates
Purpose: Understand what characters are allowed on an FQDN for SSL/TLS certificates.

Who decides what is allowed to be on a domain?
Domain Registrars decide what is allowed to be on a domain. RFC 1035 (DNS / Domain names) contains the implementation and specification rules.

What characters are allowed on a domain?
The only characters allowed are letters, digits, and hyphens.

What is an FQDN?
A Fully Qualified Domain Name is composed by www.(Hostname) entrustdatacard (Second Level Domain SLD). com (Top Level Domain TLD).

What is a Top Level Domain?
IANA, The Internet Assigned Numbers Authority, shows all the delegations for top-level domains (TLD) that are part of the FQDN. Entrust only allows the issuance of SSL/TLS certificates from a TLD registered with IANA.

What Top Level Domains are allowed?
Please see the full list under IANA.

Are underscore characters allowed on an FQDN?
In November 2018, the CA Browser Forum (Ballot SC 12) decided to sunset the use of underscore characters in domain names of SSL/TLS certificates. All underscore certificates were revoked or expired by April 30, 2019. Also, “According to with the RFC 1035 " DNS / Domain names - implementation and specification", Underscore characters are not permitted in domain names.

Are special characters allowed on domains?
Special characters are not allowed on domains by Domain Registrars.

If you have any questions or concerns please contact the Entrust Certificate Services Support department for further assistance:
Hours of Operation:
Sunday 8:00 PM ET to Friday 8:00 PM ET
North America (toll-free): 1-866-267-9297
Outside North America: 1-613-270-2680 (or see the list below)
NOTE: It is very important that international callers dial the UITF format exactly as indicated. Do not dial an extra "1" before the "800" or your call will not be accepted as an UITF toll-free call.

Country	Number
Australia	0011 - 800-3687-7863 1-800-767-513
Austria	00 - 800-3687-7863
Belgium	00 - 800-3687-7863
Denmark	00 - 800-3687-7863
Finland	990 - 800-3687-7863 (Telecom Finland) 00 - 800-3687-7863 (Finnet)
France	00 - 800-3687-7863
Germany	00 - 800-3687-7863
Hong Kong	001 - 800-3687-7863 (Voice) 002 - 800-3687-7863 (Fax)
Ireland	00 - 800-3687-7863
Israel	014 - 800-3687-7863
Italy	00 - 800-3687-7863
Japan	001 - 800-3687-7863 (KDD) 004 - 800-3687-7863 (ITJ) 0061 - 800-3687-7863 (IDC)
Korea	001 - 800-3687-7863 (Korea Telecom) 002 - 800-3687-7863 (Dacom)
Malaysia	00 - 800-3687-7863
Netherlands	00 - 800-3687-7863
New Zealand	00 - 800-3687-7863 0800-4413101
Norway	00 - 800-3687-7863
Singapore	001 - 800-3687-7863
Spain	00 - 800-3687-7863
Sweden	00 - 800-3687-7863 (Telia) 00 - 800-3687-7863 (Tele2)
Switzerland	00 - 800-3687-7863
Taiwan	00 - 800-3687-7863
United Kingdom	00 - 800-3687-7863 0800 121 6078 +44 (0) 118 953 3088