NAT configuration - DMZ zone to Trust zone

L4 Transporter

NAT configuration - DMZ zone to Trust zone

I've had a total brain fade, and am unable to figure this out. Hoping you guys can help.


Network topology is relatively simple. Firewall has three zones - outside, inside and DMZ - DMZ has a /25 of "real" Internet addresses on it. Outside has a /30, also of "real" address, and most traffic from inside is translated to the interface address of the outside zone. Inside if RFC1918 IPv4 addressing with multiple static routes to upstream networks.


I need to NAT an IP address which is in our public space in our DMZ zone - call the address - to a host which is inside my network - call it - on a one-to-one basis - no port translations, nothing. BI-directional NAT - any packet coming in to goes to, and any packet going OUT from appears to be from as far as the Internet is concerned.


Thing is, I don't know if I can do this.


I've put in two NAT rules - one translating anything going to to, and one translating anything from to - but it's not working.


I don't know if I'm screwing up the security policies related, or if what I'm asking can't be done.


So, questions for guys who have done more NAT than I have


1. Is the NAT policy I want even possible?

2. Is the methodoligy I've described right?

3. What IP address/interface should I be applying security policies (inbound and outbound) on? The translated address? The untranslated address? Both?


Can anyone shed some light for me, please? I'm scratching my head here.



L4 Transporter

Re: NAT configuration - DMZ zone to Trust zone

Hey Darren,


Can you please try the below?


Outbound Nat rule


Original packet:

  • Source - Trust
  • Source address -
  • Destination - Untrust
  • Destination Address - Any

Translated packet:

  • Source translation - Static IP
  • Translated address -


Inbound NAT rule


Original packet:

  • Source - Untrust
  • Source address - Any
  • Destination - DMZ (you got public connectivity to DMZ, right?)
  • Destination Address -

Translated packet:

  • Destination translation
  • Translated address -


Outbound Security Rule


Source Zone - Trust

Source Address -

Destination zone - Untrust

Destination address - Any

... (fill the rest yourself)


Inbound Security Rule


Source Zone - Untrust

Source Address - Any

Destination zone - Trust

Destination Address -

... (fill the rest yourself)


For testing purposes, keep your NAT & security rules at the top to avoid any conflicts.


Let me know if that works.




ACE 7.0, 8.0, PCNSE 7
L4 Transporter

Re: NAT configuration - DMZ zone to Trust zone

Thank you Sir, you are a legend.


I was applying the inbound security rule on the wrong zone, and everything was failing.


Now it's not.


Appreciate your assistance.

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