Hi Jan, okay I think you are right, that 192.0.2.15. shouldn't be considered a valid domain.
But your EBNF has been releaxed by RFC 1123, section 2.1:
The syntax of a legal Internet host name was specified in RFC-952
[DNS:4]. One aspect of host name syntax is hereby changed: the
restriction on the first character is relaxed to allow either a
letter or a digit. Host software MUST support this more liberal
syntax.
[...]
If a dotted-decimal number can be entered without such
identifying delimiters, then a full syntactic check must be
made, because a segment of a host domain name is now allowed
to begin with a digit and could legally be entirely numeric
(see Section 6.1.2.4). However, a valid host name can never
have the dotted-decimal form #.#.#.#, since at least the
highest-level component label will be alphabetic.
There are many examples, where digit-only labels are used in the DNS.
Some of them even defined by other RFCs:
411.org
1und1.com
2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.4.2.2.0.a.0.0.8.f.4.0.1.0.a.2.ip6.arpa
9.35.198.88.in-addr.arpa
0.7.7.7.0.0.7.7.0.0.7.9.4.e164.arpa
And in any case "192.0.2.15." when set in the MX record is still a
domain (and not an IP), but you convinced me, that this domain is invalid.
Defined by section 3.3.9 the "EXCHANGE" contains a domain (and not an
IPv4 address which is encoded binary in DNS).
Regards,
Matthias
BTW: Even the last sentence I have quoted is now further relaxed by the
non-ASCII TLDs we have.
Am 28.06.12 23:01, schrieb Jan Ingvoldstad:
On Thu, Jun 28, 2012 at 6:24 PM, Matthias Wimmer <[email protected] <mailto:[email protected]>> wrote:> > > Well technically I'd say that the (invalid) MX *is* pointing to a domain > name, but that domain name does not exist. > > There is no way an IP address can be in an MX record. There can just be > some (non-existent) domain, that *looks* *like* an IP address with an > additional point at the end. > > For example: AFAIK "192.0.2.10." is a perfectly valid domain name, it is > just not present in the DNS. > RFC 1035: <domain> ::= <subdomain> | " " <subdomain> ::= <label> | <subdomain> "." <label> <label> ::= <letter> [ [ <ldh-str> ] <let-dig> ] <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str> <let-dig-hyp> ::= <let-dig> | "-" <let-dig> ::= <letter> | <digit> -- Jan
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