In
<Pine(_dot_)LNX(_dot_)4(_dot_)44(_dot_)0412291528080(_dot_)2279-100000(_at_)sokol(_dot_)elan(_dot_)net>
"william(at)elan.net" <william(_at_)elan(_dot_)net> writes:
I've reread rfc1035 and have to admit that it does say that hosts can be
domains. But it also does seem to specify use of the domain as what I'd
call FQDN, i.e. for example:
<domain-name> is a domain name represented as a series of labels, and
terminated by a label with zero length.
Where as host can be a single name with no "."
I have to note that this is all inconsistant with what I've seen "domain"
used in the the many years i've been dns admin - i.e. we usually never call
end-point node a "domain" and always call it a host within a domain x.y.z
I have found RFC2181 to be very useful reading on these kinds of issues.
My understanding of the situation is:
All host names are domain names.
Not all domain names are host names.
A host is something can provide a service across the net. Depending
on the service being provided, there are restrictions on the naming
schemes and requirements for various DNS RRs.
A domain is simply a key into the Domain Name System.
The allowable characters that can be used in hosts is restricted,
while there are no restrictions on characters in domain names. (Note:
Standard representations of domain names do not allow things like "."
(dot) to be in a label, but the DNS wire format has no such
restrictions.)
The "_" (underscore) is not a valid character for a host name, but is
(obviously) valid for a domain name. Hence, underscores are used in
things like the SRV record to make sure that these domains can not be
confused with hosts.
Ok, getting back to SPF stuff, the arguments to things like the
include: and a: mechanisms should be domain names, not host names.
That is to allow things like "include:_spf.foo.com", when you don't
want to have the included record be something that could be confused
with a host.
One of the editing changes I made was to try and carefully go through
the draft and make sure every reference to "host" or "host name" was
really talking about host and not domains. And, similarly, all
references to "domain" or "domain name" are not talking about hosts.
So, this is something that I know I have been confused about before,
and I *thought* I had it figured out. If the wording in the SPF draft
is not right, please let me know.
-wayne