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On 05/25/00 at 00:19, Micaela Carr wrote:
Re: TCP/IP stack/SMTP
From: Global Homes Webmaster
Date: Thursday, May 25, 2000
Time: 1:39:50 pm
> > A secondary DNS server is simply a DNS server that gets its domain
> > data from another server, usually a primary server.
>
> Sorry to ask, but sometimes the simplest things are not necessarily that
> obvious--is it getting its data by a lookup of some sort?
A 'secondary' or 'slave' name server gets it's data through a zone file
transfer from another server. The server that the transfer comes from is
usually, but not always, a 'primary' or 'master' server for the zone.
> > To set up the DNS records for a second mail server, you first have to
> > decide how you want to use this server. If it is simply to be a
> > backup mail server, then:
> >
> > o Duplicate your existing MX record.
> > o In the duplicate record, increase the value in the Parameter 1 column.
> > o Also in the duplicate record, change the Parameter 2 column to
> > point to the name of the new mail server.
>
> Does this work like load balancing, where, if one server is not available,
> then it goes to the other server?
Kind of. The value in Parameter 1 is a preference value, with lower values
indicating greater preference. The host with the lowest value is the ultimate
destination for messages. Hosts with higher preference values should act as
back-up servers which will accept messages for the domain if the main server
is not available and then pass them on to the main server when it comes back
online.
> So--if I set it up as a NAT mail server, without having our firewall
> pointing to it, it will still recieve mail if the other is out of
> service?
If you only have one public IP address, you can only have one MX behind your
firewall, unless the firewall software has provision for multiple mail
exchangers. But then it's not a DNS issue, it's a firewall issue.
> I am truly sorry to ask such stupid questions!
Not at all. Everyone has to start somewhere. None of us has a priori knowledge
of a subject as arcane as DNS. 8^) If you are going to be dealing with DNS
on a regular basis, I'd recommend reading 'DNS and BIND' from O'Reilly &
Associates Press. It's pretty much the DNS 'bible.' There's a lot of material
specific to BIND (the *nix name server), but if you can wade through that, it
gives a very good explanation of how DNS works. And a lot of the BIND specific
material carries over to QDNS too -- mainly the stuff describing zone files,
etc.
> > Make sure you have an A record for the new mail server as well, using
> > the name you used in the new MX record.
>
> This would be on the primary as well as the secondary dns...?
Yes. All records in a zone (domain) need to be on all servers that have
authority for the zone. Secondary servers will pick up the record(s)
automagically when they perform their zone transfers.
Christopher Bort
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