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Cisco NAT question

Posted on 2013-01-30
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We have a Cisco ASA 5505 as firewall and trubble with NAT.

Firewall public IP: x.x.x.193.
Incoming traffic works fine, NAT of public ip x.x.x.194 to x.x.x.209 translates to private IP y.y.y.194 to y.y.y.209.

The problem is that outgoing traffic from local servers with IP y.y.y.194 (up to y.y.y.209) NAT through firewall via main IP x.x.x.193 not from x.x.x.194 (up to x.x.x.209).

Outgoing traffic from other local addresses in network y.y.y.0/24 routes correct via x.x.x.193.


Parts of config attached.
Cisco-ASA-conf.txt
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Question by:AITP
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rauenpc earned 2000 total points
ID: 38835327
A static NAT will normally take priority over an auto-NAT or Object nat. Although the line

nat (inside,outside) source dynamic any interface

Contains a dynamic source, it is still considered a static nat as it is not attached to a specific object.
If you do a "show nat" you will end up with at least two sections - "Manual NAT Policies (Section 1)" and "Auto NAT Policies (Section 2)"
These are processed in order, which means the static nat translating anything to the outside interface will happen before the object nat defined for servers to be translated to x.x.x.209.
You have two choices. If you change the static nat to specify its priority to be after-auto, you should be in good shape.

nat (inside,outside) after-auto source dynamic any interface

Or you can make an "any" object and do the dynamic nat there. Remember that nat is still done in order, so after making this object nat check the order of nats using "sh nat" to make sure the servers are before the all-encompassing any nat.

object network obj-any
subnet 0.0.0.0 0.0.0.0
 nat (inside,outside) dynamic interface




http://www.cisco.com/en/US/docs/security/asa/asa84/configuration/guide/nat_overview.html
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Author Closing Comment

by:AITP
ID: 38835502
Worked perfect, did first suggested solution.
Thanx!
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