On Fri, 2007-12-21 at 01:25 +1030, Tim wrote: > On Thu, 2007-12-20 at 23:06 +1100, Simon Slater wrote: > > Soooo..., going back to kindergarten..., the names I put in /etc/hosts > > were made up to describe the box on a purely internal network. Should > > the names/aliases be something different? What would/would not > > conflict with public FQDN? > Given that intro, I can't resist some fun with domain names... > > If you have SMTP server running on a machine called bluecrayons (the > machine's hostname), then that machine needs to be able to resolve > addresses in a way that makes sense to itself at start up. It'll try to > resolve the name as the server starts up. It needs to be able to > resolve those addresses, to itself, at least. > > A sample hosts file entry: > 192.168.0.1 bluecrayons.example.com bluecrayons mail smtp > > That's an IP address, a FQDN, and a list of three aliases that you might > have used (the hostname, a bog standard "mail" hostname, and another > common "smtp" hostname). The latter two aliase being things that some > people pick out of habit, but there's nothing saying you must do so, > though it does make simple sense to users to configure mail.example.com > as their mailserver). > > Your mail server can start up disconnected from a network, and that's > all it'll care about (its own addressing - that out of the interfaces > it's using, the addresses resolve). It can start up connected to a > network, and the same applies. Thus far, that's all for internal > purposes. > > However, something from outside connecting to your mail server is going > to expect a public name to match a public IP address. You could have > the same hostname/domain names, and external DNS servers use the > external IP address to the machine, and internal DNS servers giving a > different IP address to other local machines. > > e.g. An outside DNS server might associate 208.77.188.166 with > bluecrayons.example.com. Outside services would connect to you using > that FQDN or IP, and since they both resolve against each other, > externally, those outside services are happy about it. > > As for what won't conflict, don't make use of real domain names > belonging to someone else, or make up ones that might be registered by > someone at some time. > > An IP address is how you connect between A and B. A and B might have > more than one address. Which one is used depends on the networking. > The lights have just come on, physically and metaphorically! A thunderstorm has sat over the area for most of the day with power on and off all day, so I left the mail til now. Ever read all you can lay your hands on and still seemed in the dark? The light has turned on now. I realise now what I have done and how to fix it. Too late to start now. First thing tomorrow. Many thanks. -- Regards Simon
