Duel Ethernet card problems?

[Charles Steinkuehler]

Doug Bronson wrote:
> Charles,
> 
> See if you can understand my BAD drawing.

Your drawing is fine...it's your network architecture that needs help.

Also, the output of "ip route" and "ip addr" would help in diagnosing 
any configuration problems.

> [INTERNET]
>     |
> [CABLE MODEM]
>     |
> |-----------
> |  dchp
> |
> | D-LINK
> | ROUTER
> |
> | 192.168.0.135
> |----------
>     |
> |------------
> | 192.168.0.101  ROUTE:192.168.0.135
> |
> | Problem
> | LINUX BOX
> |
> | 192.168.0.1   ROUTE:192.168.0.101
> |-------------
>     |
> |-------------
> | INTERNAL
> | NETWORK
> |-------------

OK, you're not trying to hook multiple cards to the same physical 
network, but you're doing something almost as bad:  Hooking the same 
logical network (192.168.0/24) to multiple NICs (note: I'm assuming 
you're using a typical /24 or 255.255.255.0 netmask, but since you 
didn't provide the ip addr and ip route output, I don't know for sure).

It is possible to do this with proxy-arp, but configuration is not for 
the feint of heart (I know my around the low-level configuration of 
proxy-arp, but have not tried to do it in a RedHat environment).  If you 
*REALLY* want to do this, I can try to walk you through what needs to 
get setup, but you'll need to be very familiar with low-level routing 
and IP setup tools, and not afraid to diddle settings in /proc.

If there's no fundamental reason why the D-Link <> Linux network and the 
internal network *BOTH* need to be 192.168.0.0/24, I suggest you change 
the internal network numbering and run masquerading on the linux box, 
simply remove the D-Link box (assinging it's public IP to the linux box 
instead) and let the linux box do masquerading/firewalling, or change 
the linux box to having a single NIC on the internal network:

Cable-Modem
    |
D-Link Router
    |
Hub/Switch
   |   |
   |  Linux Box
   |
Other systems on internal network

If you explain a bit more about what you're trying to accomplish by 
"stacking" the DLink router and the linux box, I can probably suggest 
which network setup is most appropriate.

-- 
Charles Steinkuehler
charles at steinkuehler.net