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On 3/22/18 7:14 PM, Richard Hector wrote: Christ, why are we still discussing this. (And what does it have to do with the original question about "Federated, decentralised communication on the internet?" ... which was originally a question about how "hostname" is used by Debian) But...On 23/03/18 11:31, Dan Purgert wrote: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. RichardIt 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.That's not what I see in the RFC. The DNS only seems to care about a tree of nodes with labels, not whether a particular node represents a host or a network or something else. So if the node in question has the label "com", and "All the other nodes" consist of just the root domain (with the null label), that should be sufficient. Even just the null label followed by (empty list) should be enough. What you say may well be what was intended, but it doesn't seem specific to me. I realise practical considerations may be different, but I don't see any more requirement than that in that RFC. An FQDN defines the location of an entity in the DNS tree. For a host - which is what we've been discussing, and generally what one is talking about when talking about FQDN's an FQDN consists of both a hostname AND a domain name. (Again, in the Linux context, one is generally making the distinction between "hostname," "network name," and "fully qualified domain name" - often in the context of setting up a machine, or the "hostname" and "dnsdomainname" commands, "hostname --fqdn", or the files where such information is stored.) When it comes to hosts, it is generally understood that the FQDN consists of both the hostname and domainname, and an awful lot of protocol specs cite (and quote) https://tools.ietf.org/html/rfc1983 - the "Internet Users' Glossary" which says... Fully Qualified Domain Name (FQDN)
The FQDN is the full name of a system, rather than just its
hostname. For example, "venera" is a hostname and
"venera.isi.edu" is an FQDN. See also: hostname, Domain Name
System.
Now, arguably, "." is an FQDN specifying the very top of the DNS tree, and "com" (or "com.") specifies the top of the com domain - but who really cares. Particularly since the whole discussion started around fully qualified HOST names. Another common definition of an FQDN is that it uniquely identifies a node in the DNS tree. By that view "." is the FQDN for the top of the tree, and "com" (or "com." is the top of the .com domain - but who really cares, except for pedantic purposes. There aren't any nameservers that resolve "." or "com" or "mil" - implying that there are no records in the system for them (maybe there should be, but that's another question for another day). Miles Fidelman -- In theory, there is no difference between theory and practice. In practice, there is. .... Yogi Berra |