Do I need NAT??

jimbo7 · 11-07-2007, 02:49 AM

I have a two subnet configuration at my house.

The first subnet (192.168.1.0/24) includes my broadband modem/router.

My second subnet (192.168.2.0/24) contains all of my client computers - desktops, xbox, laptops, etc

Sitting on both these networks is my debian box (acting as a router) - it has two interfaces:
eth1 192.168.1.2 (first subnet)
eth0 192.168.2.2 (second subnet)

Now in order for my client computers to access the net I configured the Debian box to NAT using the command:

Code:

iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

(I have a script that sets up a bunch of other iptables rules as well as enabling ip forwarding)

So Now the questions!
1. Is it inefficient to have my packets being NAT'ed twice - once at the modem and once at my debian box ??
2. Should I get rid of NAT and just have the packets forwarded on to the first subnet from the second?
3. Does anyone know how would I should go about doing this?

let me know if you want me to post my full IPTABLES script.

farslayer · 11-07-2007, 08:16 AM

natting twice is redundant and not necessary. You should only need to nat at the internet connection, and if this is being done by your broadband modem, you shouldn't need to do it again in your Linux router.

jimbo7 · 11-08-2007, 01:21 AM

OK to remove the duplication of NAT, I just commented out the POSTROUTING iptables rule, then created a static route on my adsl modem/router pointing back at my second subnet.

static route settings:

Code:

Destination 192.168.2.0
Netmask     255.255.255.0
Gateway     192.168.1.2
Interface   iplan