[lug] Over my Head in a Puddle

[Zan Lynx]

On 8/14/2014 5:18 PM, Bill Thoen wrote:

> What I would like to know is how do go from "network is unreachable"
> to a working system? There's so much in place I dont know where to
> start or what to tweak, and my friend who built it has moved to Texas
> and I'm trying to learn how he did it. I'm hoping someone here can
> give me some advice on how to sort out issues between switches and
> cabling, firewalls in hardware, how to discover where the network
> problems are., etc. So... Heres the situation. what's been subtracted
> is a very nice T1, replaced by a wireless modem with built in switch,
> router, firewall, DSL, gateway, etc. From Century Link.

First, create a diagram of your network configuration.

 From what you have said I imagine that it looks something like this 
(use a monospace font if this looks funny):

                      INTERNET
                          |
                         DSL
                          |
               ----Wireless Modem----
               |                    |
            Wireless         Wired Switch Ports
               |                    |
          Windows Laptop      Linux Server

But you said that the Linux server had TWO interfaces. And I'm not sure 
it is in that diagram in the right place. If you have another router of 
some kind between the wireless access point, and the Linux Server is 
connected directly to it that might explain some of your problems.

Try updating my crude diagram to reflect your actual network setup. 
Drawing it out or just writing it clearly might help discover the issue.

For example, if you have done something like the following:

Wired Switch Ports
  eth0| eth1|
  Linux Server

then that is wrong. Unless you are doing very fancy network bonding and 
I doubt it, you only ever want one port connected to the same network.