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When to Use Interface-Based NAT and When to Use Policy-Based NAT

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Article ID: KB4106 KB Last Updated: 07 Jun 2010Version: 5.0
Summary:

When to Use Interface-Based NAT and When to Use Policy-Based NAT

Symptoms:


 

Solution:

note:This article applies to ScreenOS 4.0.0 and above.

  • Interface-based NAT can be enabled when the default trust and untrust zones are used. All traffic from the trust zone interface, bound for the untrust zone interface, will have the source IP address changed to the untrust zone interface IP.

    Interface-based NAT will only take effect on NetScreen-25, 50, 204, and 208 devices if interface ethernet1 and ethernet2 are set to NAT mode. In this scenario, traffic sourced from behind ethernet1 will be translated to the untrust zone interface IP. The same is true for traffic sourced from behind ethernet2.

    Interface-based NAT only works if interface ethernet1 is bound to the trust zone, ethernet2 is bound to the DMZ zone, and ethernet3 is bound to the untrust zone. If these interfaces are bound to any other zones, only Policy-based NAT can be used.
  • Policy-based NAT is used when you want to NAT from an interface that is not bound to the trust zone.

    Policy-based NAT is useful when you need the flexibility of changing the zone to which each interface is bound. For example, if you bind ethernet1 to a custom zone called Internet, you would need to specify Policy-based NAT from the Internet zone to the untrust zone.

    Another reason to use Policy-based NAT is if you have NetBIOS applications that need to go from trust to DMZ. You can specify the ethernet1 interface to Route mode, which allows traffic to be routed from trust to DMZ. You then specify Policy-based NAT for any traffic going from trust to untrust.


 

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