Re: [SLUG] BIND and DHCP

From: Paul M Foster (paulf@quillandmouse.com)
Date: Mon May 17 2004 - 19:13:14 EDT


On Mon, May 17, 2004 at 01:43:03AM -0400, Steve wrote:

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> On Monday 17 May 2004 12:21 am, Paul M Foster wrote:
> > In looking over a tutorial on DNS/BIND, it appears that you have to have
> > IP numbers in the file to specify machines. If you're using DHCP, these
> > number-machine correspondences can change over time. So if you're
> > running DHCP, does that mean that when numbers change, you need to
> > rewrite BIND config files and restart BIND? (All this is in the context
> > of running a DNS server for a LAN, which is continuously connected to
> > the internet.)
> >
> > Paul
>
> Interesting question.
>
> The idea is that bind is The Authority on that domain. So it needs to know,
> if anybody, what is going on. True, you could just have everything run
> off /etc/hosts, but that would not be a clean setup and would actually
> break the web standard.

<snip>

>
> Now, if you mean that dns needs to know which machine has what ip, no.
> It needs to know which particular name matches which particular ip. You can
> change ip from DHCP all day long and not worry about it.
>
> Just assign some naming convention like abc01, abc02... to each machine and
> hand it out with the ip.
>

<snip>

>
> Did that answer your question or did I not understand it?
>

Let me rethink this. Here's how it currently works.

The IP address for a given machine is assigned by the OS (Debian) when
the eth0 interface comes up. I set this up when I install the OS on the
machine. Similarly, each machine is given a specific name when I install
the OS. So currently, these things are fixed (the machine name _must_ be
fixed, for a variety of reasons).

I currently use /etc/hosts to tell all the machines on the network what
the IPs of the other machines are. But if I wanted to use BIND instead,
I could simply configure named.boot (or whatever) so that it knows these
name/IP choices I've made. Then, when a machine wants to know about
another machine, it asks BIND instead of checking /etc/hosts. Am I right
so far?

Now, let's say that instead of fixing IPs when a machine's eth0 comes
up, it asks DHCP for an IP address instead. But that means that machine
Bravo's IP address could change over time. Yet if the machine has a
fixed name but variable IP, it seems that DNS can't reliably serve it
because it there isn't a fixed IP = name correspondence. So the original
question was, if this is true, and you still wanted to run DHCP and BIND
together, wouldn't you have to reconfigure and reload BIND every time
DHCP jockeyed the IPs around?

Paul

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