[ On Saturday, February 8, 2003 at 01:38:10 (+0200), Vadim Vygonets wrote: ]
> Subject: Re: [Exim] Address rewriting vs. CNAME records?
>
> Quoth Giuliano Gavazzi on Fri, Feb 07, 2003:
> >
> > At 4:18 +0200 2003/02/07, Vadim Vygonets wrote:
> >
> > >Quoth Greg A. Woods on Thu, Feb 06, 2003:
> > [...]
> > > > "Ya know.... " there's a reason why people use unique names with
> > > > prefixes like "mail" and "www" for different services... :-)
> > >
> > >Hmm, no, I don't really see one, except convenience. Also, 'ftp'
> > >and 'www' are often CNAME records.
> >
> > because one day you might want to split those services amongst
> > distinct hosts (to spread the load/rationalise the organisation), but
> > you've got everyone used to a single name and you are stuck!
>
> As I said, convenience. In any case, I have no idea why Greg
> brought this point up, which confused me somewhat.
I think you're still forgetting that you can't have CNAME and other
record types at the same node.
In order to plan for the future you need to keep this in mind, as well
as keeping in mind how services could potentially be moved around
between servers.
You also have to think a bit about what you're doing with domain names,
and why.
One of the first things you should hopefully come to realize is that if
you don't expect to be running your very own web server on its own
unique IP address, then you have to give up on having people access your
WWW pages from the "top" domain. For example you can't get to a web
server using just the domain "weird.com" -- we decided we wanted the
ability to host our web server on a virual hosting service which means
we need the ability to delegate it with a CNAME. You can't do that for
a delegated domain though. This is of course because you _MUST_ have an
SOA record for your domain, and that means obviously that you cannot
have a CNAME there too. Less obviously you can't have different A RRs
for different services either. Things work great if you've got your
smtp, http, ftp, ns, and whatnot all on the same IP address, but as soon
as you want to move things around then you must give up on using the top
domain for everything (*). Now of course you can always choose to have one
service associated with the top domain, but you have to remember that it
has to be "delegated" with an A record, not a CNAME, and this has
implications for the owner of the address (because of the PTR
consistency checks and the number of PTRs you can reasonably have for a
given address).
(*) Because of these issues there have been various people dream about
various schemes for declaring servers for a given domain (SRV, WKS,
etc.), but none of them are widely used by any common clients. What
we've come to rely on instead are common naming conventions for hosts,
such as "www", "mail", "ftp", etc. Even the general public in any
place where the Internet has much penetration will know to prefix a
domain with "www" to get to it's web server.
--
Greg A. Woods
+1 416 218-0098; <g.a.woods@???>; <woods@???>
Planix, Inc. <woods@???>; VE3TCP; Secrets of the Weird <woods@???>
