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Well, I think Greg Wooledge is right here Let's rewind the discussion.The original context was "why do I need to have a dot in my HELO string". The reason you need a dot in your HELO string is because SMTP receivers may reject you as a spammer (or incompetent, same end result) if you do not have one. That's all. All this academic crap about nodes and empty lists is irrelevant. On 3/22/18 11:04 PM, Richard Hector
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On 23/03/18 14:44, Miles Fidelman wrote: Not sure what gets more specific than the glossary of terms used in common by all the other RFCs. Granted that it doesn't really cover the case where a node doesn't designate a "system" (though one could consider DNS as a system, in which case "." is the full name, and it doesn't have a hostname). 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.This is my point. And AFAIK DNS would happily accept an A record for com, and probably . too. (I haven't tried it in BIND; I should ...) Interesting. Of course the authoritative records would have to be on either on *.root-servers.net. or *.gtld-servers.net. (per the SOA and NS records) Might be interesting to see how bind would work if you created a local record. 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.When talking about specs and RFCs (which maybe only I was), surely pedantic purposes are what it's all about? Well yes, but if one wants to get pedantic, one has to note that the standards are explicitly vague about some things. Notably: RFC-1034, DOMAIN NAMES - CONCEPTS AND FACILITIES 3. DOMAIN NAME SPACE and RESOURCE RECORDS 3.1. Name space specifications and terminology Starts with "The domain name space is a tree structure. Each node and leaf on the tree corresponds to a resource set (which may be empty)." and goes on to say "The domain name of a node is the list of the labels on the path from the node to the root of the tree." From there, and in other RFCs, there is some specificity ("MUSTs" & "SHOULDs"), but there is also language like "By convention," and a lot of "MAYs". I.e., one can only be pedantic up to a point. And then one has to accept that there are general understandings, as well as wide variances in the way different people & software implement things. So there are. I stand corrected.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).There might not be A, AAAA or MX records, but there are certainly servers, and they serve at least SOA and NS (and RRSIG) records for all 3 of those. Cheers, Miles -- In theory, there is no difference between theory and practice. In practice, there is. .... Yogi Berra |