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Cisco ASA 8.3 - No NAT / NAT Exemption

As we all know Cisco`s new ASA version 8.3 brings massive changes in NAT. This article describes and explains how NAT exemption (no NAT) is now configured. 

Below provides examples of both pre and post 8.3 no NAT configurations. 

Example Details

  • Local LAN - 192.168.0.0/24
  • Remote LAN - 172.168.0.0/24
  • Traffic is arriving on the inside interface and leaving the outside interface.

Pre 8.3

Pre 8.3 a access-list was configured to define the source network and destination network. This access-list is then referenced in a NAT 0 statement to ensure all traffic traveling from the local LAN to the remote LAN is not NAT`d. 

access-list NO-NAT permit ip 192.168.0.0 255.255.255.0 172.16.0.0 255.255.255.0
nat (inside) 0 access-list NO-NAT

Post 8.3 

Within 8.3 and later the networks are defined as objects via the use of object groups. These object groups are then referenced within the NAT statement to define both the pre and post NAT (real / mapped) addresses.

object network LOCAL_LAN
subnet 192.168.0.0 255.255.0.0

object network REMOTE_LAN
subnet 172.16.0.0 255.255.0.0

nat (inside,outside) source static LOCAL_LAN LOCAL_LAN destination static REMOTE_LAN REMOTE_LAN

To make things clearer you can see the structure of the NAT statement below.

nat (real interface,mapped interface) source static [real_object] [mapped_object] destination static [real_object] [mapped_object]

Tags: ASA

About the Author

RDonato

R Donato

Ricky Donato is the Founder and Chief Editor of Fir3net.com. He currently works as a Principal Network Security Engineer and has a keen interest in automation and the cloud.

You can find Ricky on Twitter @f3lix001