M-1 Cable Modem, Linux

["Carl Patten" <cpatte@trimodalinc.com>]

Funny, it was easier to share my 2-way cable modem connection under Linux
than under Windows 95.  Wingate worked fine for sharing access when I had
just the 1-way cable modem and a single Ethernet card.  Moving on to 2-way,
however, it didn't like the 255.255.255.128 subnet which DHCP assigned my
Ethernet card, and attempting to use two Ethernet NICs to bypass the problem
destabilized the box.

Instead, the following worked great for me.  I wanted a firewall anyway,
so...

(1) Bought bare-bones Pentium 75 box with Ethernet NIC.

(2) Installed my original Ethernet NIC in it (so it has 2 NICs).  This is
because MediaOne DHCP will only assign an IP address to a NIC for which they
have the MAC address.  This is my "external net" NIC.

(3) Loaded RedHat Linux 6.1 (because I'm familiar with it).  Its Kudzu tool
did a great job of detecting and configuring both NICs.

(4) Assigned a static IP to the "internal net" NIC, let the "external net"
NIC be configured by DHCP.

(5) Plugged the "external net" NIC into the cable modem using a cross-over
cable, and plugged the "internal net" NIC into my hub.

(6) Ran pmfirewall to get a fairly solid ipchains firewall/masquerading
config.  This free tool is available at http://www.pointman.org .

(7) Set default gateway on the client PCs to the IP of the "internal net"
NIC, and set DNS to that of the MediaOne DNS servers.  Assigned static IPs
to each client (only had 2).

Everything worked.  Next step is to get a domain name and register it with
Just Linux (http://www.justlinux.com/dynamic_dns.html) so I can have a
static domain name even though my DHCP-assigned address may change!

--
Carl Patten
Systems Administrator
Trimodal Inc.
"Having more fun at home than at work, at least today!"