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Re: How do I troubleshoot my DHCP server and eth1 configuration?

on 11:27 Tue 01 Mar, Jason Hsu (jhsu802701@jasonhsu.com) wrote:
> My hardware setup:
> Modem -> (eth0) -> Firewall/server computer (Debian Lenny, Shorewall,
> DHCP3 server) -> (eth1) -> Ethernet switch -> (eth0) -> Main computer

> I did successfully access the Internet before from my main computer
> with this setup.  I used the instructions at
> http://www.cyberdogtech.com/firewalls/ (with some adaptations for
> Lenny) to set up Debian Lenny and Shorewall.  I used the instructions
> at
> http://failserver.nl/blog/2009/03/how-to-install-a-dhcp-server-in-linux-debian-lenny/
> to set up a DHCP server.
> Unfortunately, I made an unsuccessful attempt to upgrade to Squeeze
> and had to reinstall Lenny.  Now I'm unable to connect to the Internet
> from my main computer with this setup.

Is NAT forwarding enabled on the firewall/server?


If it can access the Internet, and you can ping the firewall from the
inside, I'd suspect the problem is packets not traversing the firewall.

What makes you suspect that DHCP is the issue?
> I'm pretty sure that it's just one or just a few minor little details
> that are stopping my main computer from accessing to the Internet with
> this setup.  When I connect my main computer to the modem and restart
> its eth0 interface, I can connect to the Internet, so it's not an
> Internet connection problem.  My firewall/server computer has no
> difficulty accessing the Internet when connected to the modem and with
> eth0 properly activated, so I don't think there's a hardware issue
> there.  I tried uninstalling shorewall on my server computer, but that
> didn't solve the problem, so I don't think the firewall was blocking
> Internet access.  Thus, the only thing I can think of is a problem
> with my DHCP server settings or its eth1 settings.
> How do I troubleshoot a DHCP server and the eth1 configuration?  

If you're handed a DHCP lease when you bring up the desktop interface or
run dhclient against it, you're golden.

'dhclient -v eth0' should tell you what's going on.  You'll also see
queries and leases in both the client and server logs.

Dr. Ed Morbius, Chief Scientist /            |
  Robot Wrangler / Staff Psychologist        | When you seek unlimited power
Krell Power Systems Unlimited                |                  Go to Krell!

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