PGNd <[email protected]> wrote:

> I've setup a DHCP connected linux box.  It runs Shorewall.
> 
> [net]
>  |
> ------------------------
> EXT: DHCP Client
> Uverse/ATT modem (bridge mode)
> INT: DHCP Server & WebServer @ http://192.168.1.254
> ------------------------
>  |
>  |
> ------------------------
> EXT: DHCP Client -> IP == 1.2.3.4
> Linux Router/Firewall (shorewall)
> INT: 192.168.1.100
> ------------------------
>  |
>  |-------------------------------|
> -------------------     -------------------
> EXT: 192.168.1.10       EXT: 192.168.1.20
> Linux Laptop            Linux MailServer (temp)
> -------------------     -------------------

Tom has beaten me to it - you have an invalid IP configuration since the subnet 
between modem and firewall is the same as your internal network. Thus it's not 
possible to correctly route traffic to allow internal devices to access the 
modem.

What you need to do is renumber one or other of the networks so that the 
subnets do not overlap.
Once you have done that, you'll find that the modem is directly reachable - 
though you may need to relax your RFC1918 filtering*.

If you don't change your masq config, then the modem will see traffic coming 
from your external address. You can alter that by specifying (from memory) 
"net:!192.168.2.0/24" in your masq config file (assuming you'd changed the 
modem to be in the 192.168.2.0/24 subnet).

* If you are still using (from memory) norfc1918 which IIRC is deprecated, then 
you'll need to remove it and apply rules. You need to add permit rules for the 
outside private network. So you'll need rules like :
permit lan net:192.168.2.0/24
deny lan net:192.168.0.0/16
deny lan net:172.16.0.0/12
deny lan net:10.0.0.0/8

You are filtering RFC1918 traffic on egress aren't you ?


NB - I had a similar setup at one time, with an ADSL modem on RFC1918 address 
and router getting address from ISP by DHCP.


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