2 NIC machine questions (for internal firewall)

[SgtB]

Here's the situation (I'll try ot be brief). I'd like to set up an internal firewall right before our WAN router. Here's the catch. Both NICs will have IP's sitting on the same network. Let me draw this out. It may help.

[WAN]-><-[Router-10.10.10.1]-><-[Ext interface on FW-10.10.10.2]<IP Forwarding enabled>[Internal Interface on FW-10.10.10.3]-><-[LAN-10.10.10.x]

Is this situation possible? I'd like to have all WAN traffic filtered by the firewall. All inbound WAN traffic hits the router, gets passed to the firewall. Firewall filters, then if accepted, passed on to the LAN. Same goes for outbound traffic from LAN to WAN.

Changing IP's on the router or LAN is not an option. Access-lists on the Router are not an option either. I was thinking of using an open source *nix OS since cost is an issue.

Any ideas?
Thanks for any replies!

 

[jgercken]

What do you mean by same network? Both nics plugged into the same hub? Sure that'll work. The interfaces/NICs will just discard packets not on their subnet (little extra load though).

Just use a /24 or class C netmask on the subnets eg 10.10.10.1 255.255.255.0

-Jeff
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[SgtB]

jgercken,

Thanks for the reply. Maybe I didn't explain my situation properly.
One interface will sit on hub connected to the LAN and the other interface will sit on a different hub that's connected to the router's ethernet only.
I used the term &quot;same network&quot; to show that both interfaces on the firewall will have a 10.10.10.x IP, and that the LAN and router (both sides of the FW) are also on the 10.10.10.x scheme.

I hope this clarifies things a little better.

 

[SgtB]

Here's a diagram of what I'm talking about.
Hope this helps.