Re: [cobalt-users] Virtual site DNS question

[Jeff Lasman <jblists@xxxxxxxxxxxxx>]

At 11:40 AM 2/22/00 -0700, you wrote:

> For each virtual domain, my understanding is I need:
>
>  * two A records (mydomain.com, www.mydomain.com)
>  * one PTR record (IP address = mydomain.com)
>  * one MX record (mail.mydomain.com)

If you've got an MX record pointing to <mail.mydomain.com>, then you also 
need an A record for <mail.mydomain.com>, so it'll resolve.

We also install A records for other common server names, i.e.: 
<smtp.mydomain.com>, and <pop.mydomain.com>, to give our users added 
flexibility in setting up servers.

And we install a CNAME record for ftp, pointing to www.

Why you ask?  Even though CNAME records can be used for any records not 
pointed to by MX, and therefore we only need one A record, pointing to 
<mail.mydomain.com>, and all the rest can be CNAME records, CNAME records 
take one step longer to resolve, so things go a little faster, then, if we 
use A records.  Why, then do we use the one CNAME record, for ftp, pointing 
to www?  Simple, so the zone file will have one example, to be used as a 
template if we or the customer need to create more in the future.

In general, except in huge zone files with lots of services all pointing to 
the same IP#, you're better off using A records, though of course it makes 
it a bit more time consuming to make changes.  CNAME records are best used 
when you're pointing to a domain or system whose IP# could change, and over 
which you have no control.

For example, if I'm going to buy outsourced usenet news connections from a 
server at <news.newscompany.com>, I might use a CNAME record pointing 
<news.mycompany.com> to <news.newscompany.com>.  That way, if they 
renumber, I'm still pointing to the right place.

> My question is: do I need a PTR record for each virtual domain,
> since they all share the same IP, or just one PTR record in my
> main DNS settings? (for the host, etc.) Thanks in advance.

Only one PTR record for each IP#, only if reverse delgation has been 
delegated to you (which it usually isn't, if you've got only a few IP#s), 
and only in it's own zone file for your own segment of the <in-addr.arpa> 
domain.

If that doesn't make sense <wry grin>, then read O'Reilly's "DNS and BIND", 
use the RaQ's web-based gui interface, and/or get a consultant 
<smile>.  Robust DNS is the most important part of your operation there is; 
it's even more important than keeping your webserver running.

Jeff

--
Jeff Lasman <jblists@xxxxxxxxxxxxx>