[TriLUG] newbie needs help with IP setup, part 1: DHCP

[Brian Henning]

TWC is probably not allowing you more than one public IP at a time, and
probably once your laptop grabbed it the first time, your laptop's MAC
was stored in the cable modem, preventing any other MAC from obtaining a
lease.  Power-cycling the modem should clear its MAC cache and allow a
different device to request an IP (but still only one device at a time).

So, one thing you didn't specify is whether the modem is configured as a
bridge (handing out public IPs to connected devices) or a router
(handing out private [probably 192.168.x.x] addresses to devices).  My
argument is null for the latter, but worth examining for the former.

My Motorola Surfboard TWC modem is only a bridge, to my knowledge.

HTH,
~B

-----Original Message-----
From: trilug-bounces at trilug.org [mailto:trilug-bounces at trilug.org] On
Behalf Of Tom Roche
Sent: Tuesday, December 04, 2007 4:55 PM
To: trilug at trilug.org
Subject: [TriLUG] newbie needs help with IP setup, part 1: DHCP


I'm trying to setup a POS for my food co-op. That will ultimately
require static IP (more later), but for current testing DHCP should
work. Unfortunately I'm not getting even that, and I'd appreciate your
help. Note that the following is all barebones because we're poor and
we're trying to do this cheap (and we're all volunteers).

I've got a box setup with latest Ubuntu Server Edition, commandline
only. The install looks good: I can `lynx http://localhost` and see
the POS interface. Both the box and my laptop are connected (via cat5)
to an old-school 10/100 hub, which is itself connected (via cat5) to a
TWC cablemodem. The laptop DHCPs and IPs just fine. So I su'd into the
box and

0 cp /etc/network/interfaces /etc/network/interfaces.orig

1 edited /etc/network/interfaces from

- auto eth0
- iface eth0 inet static
- blah
- blah
- blah

to

+ auto eth0
+ iface eth0 inet dhcp
+ # blah
+ # blah
+ # blah

2 /etc/init.d/networking restart

but that doesn't work: scroll includes

 > DHCPRELEASE on eth0 to 192.168.1.1 port 67
 > send_packet: Network is unreachable

and finishes with

 > No DHCPOFFERS received.
 > No working leases in persistent database - sleeping.

Just to rule out a connection problem, I disconnected the cables at my
laptop and back o' the box and swapped them: laptop was fine with
that.

What am I doing wrong? Your assistance is appreciated, esp commandline
help. (For the application I'd prefer not to put X on the box.)

TIA, Tom Roche <Tom_Roche at pobox.com>

-- 
TriLUG mailing list        :
http://www.trilug.org/mailman/listinfo/trilug
TriLUG Organizational FAQ  : http://trilug.org/faq/
TriLUG Member Services FAQ : http://members.trilug.org/services_faq/