some networking questions, I'm slightly confused

Darrell Shandrow nu7i at
Wed Dec 5 22:19:57 EST 2001

Hi Greg,

I have stayed out of this until now because I haven't really had any time 
to respond properly.  My days are usually quite long lately.  Anyhow, I am 
a sys admin for a regional ISP; perhaps, I can help you.

A domain is registered through a registrar like Network Solutions or  When the domain is registered, part of the required 
information includes the IP addresses for the primary and secondary name 
servers.  This information is then added to what are known as the root 
servers, which tell the entire world which primary and secondary name 
servers know how to answer lookup questions about your domain.  In other 
words, the root servers delegate authority to the specified primary and 
secondary name servers to answer questions concerning your domain 
name.  You could run one or both of these name servers yourself or have 
someone else do DNS.  It sounds like you are having someone else do primary 
and secondary DNS.  As I'm sure you already know, DNS is the domain name 
system, which points domain names to IP addresses, and which allows us to 
do neat things like browse to and send mail to 
nu7i at instead of having to know all kinds of awful IP addresses 
just to perform the simplest of functions on the Internet.  So, DNS points 
a domain name to an IP address, but how does it work?  DNS information 
about a domain name is handled by name servers in the form of zone 
files.  Your domain exists as a zone file on the primary name server, and 
the secondary name server is usually set up as a slave to the primary.  In 
other words, the secondary name server gets its information (the zone file) 
from the primary name server and holds onto it, just in case the primary 
name server is unavailable for some reason.  The domain name system is 
really a very large, world wide distributed database.  A domain name 
contains various types of information which is managed in the form of 
various types of records.  The first type of record is SOA, which stands 
for start of authority.  This just specifies your primary and secondary 
name servers.  You see, if things were set up a certain way, your primary 
and secondary name servers could actually delegate authority for your 
domain to still other name servers, but this is not common 
practice.  Another important record type is the A record.  This is the 
address record, and your domain could have multiple A records, depending on 
how many subdomains you have set up.  For example my domain name servers 
have an A record for which points to  There is 
also another A record for, a subdomain, which also 
happens to point to the same IP address, though it could just as easily 
point to another IP address.  Another somewhat related record type is a 
CNAME, which stands for canonical name.  These records are used like 
aliases to point subdomains to other domains.  For example, I did use a 
CNAME record to point to, which means it also 
has the IP address  Yet another important record type is 
the MX record.  MX stands for mail exchanger.  E-mail software uses these 
records when figuring out how to deliver e-mail on the Internet.  These 
records, numbered by priority, tell mail delivery software where mail 
should go when destined for a particular domain.  For example, my first MX 
record priority for (which is MX 10) points to  That is ultimately pointing to the Sendmail server 
which runs on the IP address  But, again, this could have 
just as easily pointed to any Sendmail server which was configured to 
accept and deliver mail for the domain.  Additional MX records 
can be defined so that, if the server specified in the first priority MX 
record is unavailable for some reason, mail delivery software will try a 
second, third, fourth and so on server until it can deliver the mail.  I 
could, if configured properly, have a MX 20 pointing to yet 
another Sendmail server, which would be able to receive mail for in the absence of the primary mail server.

Finally, there is reverse DNS.  This does the reverse of the domain name 
system; it translates IP addresses back to domain names.  You definitely 
want to have your DNS administrator set this up for your domain, because 
certain FTP sites, web sites and other types of services on the Internet 
use reverse DNS information for security purposes; they want to see that 
your forward DNS and reverse DNS point to the same place, or they may also 
want to verify that you have a domain which is or is not registered in a 
certain part of the world.  In my example, performing a nslookup on the IP 
address will tell you that it reverses to, 
which is a valid subdomain pointing to that same IP address.

Anyhow, this will either help you or confuse you.  Please let me know if I 
can help you with specifics.


At 06:38 PM 12/5/2001 -0600, you wrote:
>Well, I'll actually be running a mail server for the building in which I live.
>Instead of being regularly payed, my current connection will be free, and 
>I'll get a second free connection
>They're running t1 over here through this HP networking gizmo that
>plugs into the phone jack, and has an rj45 jack on it.
>The reason I'm asking about the dns stuff is because
>when I told the guy that I've looked at the mail admin docs, and am 
>seriously considering running the server,
>his response to me was:
>"so, I'll need to get you a domain with primary and secondary dns servers."
>I said yes to this, but am carious about how his dns servers will know 
>where I exist
>since he didn't ask for the name of my box.
>I guess when he tells me he's got things set up,
>my first question to him will be,
>"what name do the dns servers know my machine by?"
>He's macroslop licensed, but not meaning to brag,
>I get the impression that I may know more then he does without a license.
>In case some of you reading my post now are remembering a few of my other 
>posts, I decided
>that getting my own domain name wasn't worth it.
>He said that I could run a small web server here if I want. So, I don't 
>think he'd
>have a problem with me running it as http://mybox.domain.
>This whole thing started when I got my service, and he came here to get it 
>all setup.
>Not only was he impressed that I was the only one in the building so far 
>running anything other then windblows, but that it was Linux.
>After my configuring tcp/ip both in windows and in Linux while he just 
>watched me do it and gave me my ip address and all the other stuff,
>I asked if I would get a mail account.
>He said no, because there is no body to run one yet.
>Then he tentatively asked if I would be willing to perhaps do it, I said 
>I'd read the mailadmin docs and think about it,
>and you know the rest.
>He's also looking to hire someone to run apachee.
>But, I'm not touching that for now (grin).
>Sorry for the long and personal post, but since Geoff asked,
>I figured that some other people on this list may be wondering
>why I'm asking theese questions, some of which may sound
>dumb, but are for the most part so that I could make sure that what
>I know is actually correct.
>On Thu, Dec 06, 2001 at 09:29:48AM +1000, Geoff Shang wrote:
> > On Tue, 4 Dec 2001, Gregory Nowak wrote:
> >
> > > 1. Say there is a primary and secondary dns servers on a domain 
> called mydomain.
> > > Say also that there is a machine called mybox.
> > > Also, I have ip addresses for primary and secondary dns servers on 
> mydomain.
> > > Assumming all of the above, and assuming that I have permission to 
> officially be on mydomain which is a valid internet domain,
> > > what do I do on mybox so that it would be resolvable
> > > as mybox.mydomain on the net?
> >
> > Nothing.  It's the primary and secondary DNS servers that control how your
> > host is resolved, not your box.  As long as mybox has the IP address that
> > and think it has, you should be good to
> > go.
> >
> > > 2. Say that I have to nics with 2 static ip address for the outside 
> world.
> > > How do I set things up so that my box would use both
> > > nics for outside access instead just either one nic or the other?
> >
> > As Chris said, what comes in where will depend on what address it is sent
> > to.  What goes out where depends on a few things.  If you want to use one
> > interface to access a particular host or network, you can set up a route
> > accordingly.  If you want to access everything with both, you might be able
> > to put 2 default routes (i've seen it done but don't know if it works and
> > if it's supposed to work).  I saw you've been looking at bonding which
> > might also work, but I don't know about it.
> >
> > Can I ask, why you have 2 NICs?  Is it just to get 2 addresses or are you
> > connected to 2 networks?
> >
> > Geoff.
> >
> >
> >
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