[CLUE-Tech] DHCP and DNS

[David Anselmi]

Roger Frank wrote:
[...]
> So how do I lookup the IP address of a machine that has gotten it
> through DHCP? I know the (fixed) address of the DNS server
> (192.168.1.3) but that doesn't seem to have local addresses.

You could ask your IT people.  If they aren't completely swamped they 
might be willing to do more than you expect.  A friendly relationship 
with them might get you a long way.

If you do talk to them, be clear about your requirements.  Don't say "I 
need static IPs," say "I need to use NFS."  Or even "I need these 
machines to share these directories."

What you're asking for is dynamic DNS.  Windows Active Directory does 
this easily and it is replacing WINS.  Do the Windows machines at your 
school update DNS when they get an address?  If so you should be able to 
update it from your machines as well.  I say should, I don't know how 
stable *nix clients are for that.

It might be possible to set up your own local DNS that you could update 
dynamically.  It would only serve your lab and only be authoritative for 
names in your lab.

If Samba has something to wire WINS into *nix lookups you might try that 
too, and run a WINS server.  I have a Linux box on a Windows network and 
it can't find machines by name.  But all the Samba tools Just Work(tm).

How does your lab connect to the district?  I assume there's a router 
between your school and the rest, is there a router between your lab and 
the school?  If these were Windows machines, would they be part of the 
"official" domain?

Why is your lab hooked into the rest of the network?  It could exist 
standalone and I'll guess that what you want most is Internet access. 
In that case you could set up your own router and NAT to the school 
network.  That probably is the easiest solution.  Linux does routing, 
NAT, multicast routing, and DHCP relaying well (ok, dhrelay is kind of 
braindead, but so is DHCP).

Even if your lab is part of the school subnet and you want it to stay 
that way, you could run your own static subnet on top of the dynamic 
one.  Give each machine two IPs, one static and one dynamic.  Each 
machine will have and eth0 and an eth0:1.  Run your own DNS for the 
static addresses (or use hosts files).  Your static subnet will not be 
routable, and having two on the same LAN segment is a chance for 
confusion, but otherwise it should work fine.  You'll want to be careful 
that static addresses don't leak to the "official" network -- don't do 
reverse lookups to the district DNS server or advertise routes to your 
subnet.

Sounds like a fun problem to work on.  Let us know how else we can help.

Dave