Cisco Pix DMZ without NAT, LAN with NAT

Posted on 2007-11-20
Last Modified: 2011-04-14
Good evening all.
We have a CIsco Pix 515E with three interfaces, Inside (, Outside and DMZ (  We have a public /29 IP range ( for this example).  I am not sure if this is even possible but its worth a try.  The Pix is all setup and working no problem. Our LAN connects to the internet (shown IP and DMZ without issues, our webmail ( is published with the DNS extension to allow internal access without requiring an internal DNS entry etc.

We now need to run an application in the DMZ that must bind to the public IP Address ( so we require the NAT to be disabled on the DMZ only.  I have had a play with the config but because for it all to route correctly the DMZ interface needs the IP Address however this fails because it conflicts with the outside interface.

After thinking about this for a good while my feeling is that a second pix will need to come in and be placed in front of our existing Pix but run without NAT but still allow our machines to be firewalled.  Is there a way of running the DMZ purely on our public IP range rather than a private one NAT'd.  I have googled, gone through Cisco docs etc and can only find examples for running NAT or no-nat but not both.  If the only way is with a second Pix then fair enough but if it can be done without that would be a bonus.


Question by:Sword_Fish
  • 2

Accepted Solution

Sword_Fish earned 0 total points
Comment Utility
Realised this morning that yes we will need a second pix to run

Leased Line router ---- transparent pix --- switch --- routed pix.  

The switch would also have the public IP'd interfaces of the servers.  The Cisco support docs also appear to support this
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Expert Comment

by:Alan Huseyin Kayahan
Comment Utility
   Hi Sword_Fish
       "We now need to run an application in the DMZ that must bind to the public IP Address ( so we require the NAT to be disabled on the DMZ only."
        For achieving this, you dont need a second pix and you dont need to disable NAT.
        If you want to address translate your all DMZ network to in outside, you need following
        nat (DMZ) 2
        global (outside) 2
        access-list outside_access_in permit tcp any host eq yourapplicationsport
        If the application runs on 1 Server/computer in DMZ (lets say that its ip is, do the following
        static (DMZ,outside) netmask 0 0
        access-list outside_access_in permit tcp any host eq yourapplicationsport


Author Comment

Comment Utility
Unfortunately the server in the DMZ has to be physically assigned in Windows the IP address  We have got hold of a second pix to run purely in transparent mode and will mount a switch between pix1 and pix2, plugging the server into this switch.

Statics don't work (I tried) because the IP address of the windows server must be

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