Richard Hector wrote: > On 23/03/18 01:17, Greg Wooledge wrote: >> [...] >> RFC 1594 <https://tools.ietf.org/html/rfc1594>: A Fully Qualified >> Domain Name (FQDN) is a domain name that includes all higher level >> domains relevant to the entity named. If you think of the DNS as a >> tree-structure with each node having its own label, a Fully Qualified >> Domain Name for a specific node would be its label followed by the >> labels of all the other nodes between it and the root of the tree. >> >> For example, for a host, a FQDN would include the string that >> identifies the particular host, plus all domains of which the host is >> a part up to and including the top-level domain (the root domain is >> always null). > > Thanks - Having read that paragraph of the RFC, it doesn't seem to > require any particular number of levels, only that all that exist are > present. > > Richard
It requires two "levels" 1. the TLD itself 2. the named host Therefore, "com." (that is, the TLD 'com') is not a valid FQDN. However, "a.com." (that is, the host 'a' on the 'com' TLD) is a valid FQDN. NOTE -> the trailing dot is only required in DNS entries, general internet usage (email, [web|ftp|nntp|etc] services, etc.) do not require it to be used (although, a quick test to slashdot, google, and sparkfun; all three resolved properly with the trailing dot included). -- |_|O|_| Registered Linux user #585947 |_|_|O| Github: https://github.com/dpurgert |O|O|O| PGP: 05CA 9A50 3F2E 1335 4DC5 4AEE 8E11 DDF3 1279 A281
