[dns-operations] Delegation to IPs?

Peter Koch pk at DENIC.DE
Tue Mar 13 13:18:25 UTC 2007

On Tue, Mar 13, 2007 at 09:04:18AM -0400, Joe Abley wrote:

> It's lexically legal, of course. There's nothing in the protocol  
> which prohibits numeric labels. So you can expect your authority  

right, but splitting hairs (or host vs. domain names) again, here's RFC 1123,
section 2.1:

	However, a valid host name can never
	have the dotted-decimal form #.#.#.#, since at least the
	highest-level component label will be alphabetic

Sadly enough, these "numeric domains" sometimes actually work, at least I've
seen that for MX targets when the MTA did not directly use the low level
resolver but submitted the MX target to a function like gethostbyname()
that translates the "name" into an IP address bypassing the DNS.
(``The host SHOULD check the string syntactically for a dotted-decimal number
   before looking it up in the Domain Name System.'')


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