[ On Thursday, January 1, 2004 at 03:29:26 (+0100), Kjetil Torgrim Homme wrote: ]
> Subject: Re: [Exim] Inbound Hosts without valid rDNS
>
> On Wed, 2003-12-31 at 22:47, Greg A. Woods wrote:
> > There is _no_such_thing_ as an "official" or "primary" hostname in the
> > DNS, nor can there ever be any such construct, _by_its_very_design_.
>
> but _every_ Unix host has such a primary hostname, it's the one you get
> when you call gethostname(2) or uname(2). similarily, Windows machines
> have _one_ primary name associated with them.
Obviously you do not understand the DNS well enough if you're making
such a fundamental mistake as that above.
Unix and M$ Windows are simply an operating system, and though most
modern Unix and all modern M$ Windows implementations have a TCP/IP
networking stack and can run applications such as SMTP mail servers
which use the DNS for resolving hostnames and addresses, the OS concept
of "hostname" is totally and completely unrelated to the DNS.
gethostname(2) and uname(2) are not in any way related at any level, not
even conceptually, with the DNS. The kernel hostname is simply an
arbitrary string -- an identifier the kernel can use for itself when it
cries out in pain.
It is simply a common convention that the kernel's idea of a hostname
usually match a DNS hostname that happens to resolve to an IP address
which the host will answer to on one of its interfaces. However it's
still not uncommon for the kernel hostname to be a UUCP name which does
not match any of IP address on any of the host's own network interfaces.
Let me repeat again:
There is _no_such_thing_ as an "official" or "primary" hostname in the
DNS, nor can there ever be any such construct, _by_its_very_design_.
If you don't understand this axiom then please at least try to accept it
as the fundamental truth about the DNS that it is.
--
Greg A. Woods
+1 416 218-0098 VE3TCP RoboHack <woods@???>
Planix, Inc. <woods@???> Secrets of the Weird <woods@???>
