virtual domains and zone files

Andrew andrew at arda.homeunix.net
Tue Dec 2 04:09:48 UTC 2003


Well, I did open a can of worms, didn't I? 'Virtual domain' is such a 
common term when referring to email delivery I didn't think twice about 
using it here. If there is a more acceptable term to DNS admins, I'd 
like to know what it is because, right now, I have no other way to label 
what I'm talking about.

The zone file I posted really is for the arda.homelinux.net zone, 
honest. It's purpose in life is to tell hosts on my network that if 
someone sends mail to user at arda.homelinux.net, use 
callisto.arda.homeunix.net as the mail exchanger. There are no A records 
in this zone file because there are no hosts with the FQDN of 
<hostname>.arda.homelinux.net on my network. The A records for io, 
europa, and callisto reside in the arda.homeunix.net zone file. Which is 
what you might expect given that their FQDNs all end in arda.homeunix.net.

All I wanted to know is whether the SOA and NS records in the 
arda.homelinux.net zone file are really necessary. Having thought about 
how hosts determine where to send mail addressed to 'virtual' domains, I 
think that they are. Of course, the whole purpose of posting my question 
was to allow people more knowledgeable than I to confirm or deny my 
suspicion.

So I suppose I've answered my own question. I'm surprised at how much 
consternation my question has caused, though, given the wide use of 
'virtual' domains in email delivery and the fact (as far as I know) that 
DNS must be set up specifically to allow such delivery.

For those who are interested, all my zone files and my named.conf file 
are posted on my web site. Go to:
http://www.arda.homeunix.net/dnssetup.shtml

Andrew

Andrew wrote:

> My mail server hosts a virtual domain that does not include any hosts in 
> it. Here is the zone file I use with this domain.
> 
> # cat /etc/namedb/master/arda.homelinux.net.zone
> $ORIGIN .
> $TTL 10800      ; 3 hours
> arda.homelinux.net      IN SOA  europa.arda.homeunix.net. 
> postmaster.arda.homeunix.net. (
>                                  20030416   ; serial
>                                  10800      ; refresh (3 hours)
>                                  3600       ; retry (1 hour)
>                                  604800     ; expire (1 week)
>                                  3600       ; minimum (1 hour)
>                                  )
>                          NS      io.arda.homeunix.net.
>                          NS      europa.arda.homeunix.net.
>                          MX      10 callisto.arda.homeunix.net.
> 
> As things stand now, I can deliver mail to user at arda.homelinux.net but I 
> would like to know if this zone file looks reasonable or if there are 
> elements that don't need to be there.
> 
> Andrew
> 
> 
> 
> 




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