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Cisco ASA PIX Multiple NAT Statements

Posted on 2014-12-10
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Last Modified: 2015-01-07
I have a host on which I have IIS running and it therefore needs to be publicly accessible on TCP80/443.

I now also need this host to be accessible over an IPSec VPN tunnel, also on TCP80/443.

The remote end requires me to source NAT my host and I therefore need the following.

1. Host A NATs to public IP x.x.x.x under normal circumstances.
2. Host A NATs to private IP y.y.y.y only when passing traffic over the IPSec tunnel.

How do I configure this ?

I originally had a static NAT statement mapping host A to y.y.y.y. If I try to add a second NAT statement using an ACL which specifies host A and the remote subnets I get an overlap error.

If I remove both statements and enter the NAT statement with the ACL first followed by the statement mapping host A to y.y.y.y I get the same error.

How can I configure it to NAT to different IP addresses based on different destinations ?

TIA
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Question by:ccfcfc
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Expert Comment

by:Spartan_1337
ID: 40491814
OK. You definitely need to NAT from public to Host A, that's a given.
Why did you feel you needed to NAT the IPSec? As long as you enable Reverse routing, it will forward those packets out the same interface.  The ACL you configure as required but what happens to the remote network with the NAT statement removed? Is the tunnel configured to pass that traffic across? Can you show any logs?
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Author Comment

by:ccfcfc
ID: 40491850
The remote side has imposed a subnet on us.

We need to NAT to addresses within this subnet that they have provided us for traffic going over the IPSec tunnel to meet with their addressing requirements, so I don't have the option of not doing this.

There isn't any logging to show yet as when I try to enter the second NAT statement I get the error message about an overlap.
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Expert Comment

by:Jan Springer
ID: 40491916
You need to configure (nat exemption) an access-list and apply it to your NAT statement so that the IP addresses or subnets listed in the ACL are exempt from the NAT.

The configuration is different for 8.2 and earlier and 8.3 and later.
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Author Comment

by:ccfcfc
ID: 40492659
NAT exemption is what I would normally be applying to traffic passing over an IPSec tunnel.

This isn't NAT exemption - the third party at the remote side is dictating the address that I need to NAT my side to. I cannot just NAT exempt it to use my private IP addresses - I have to NAT it to the addresses that I have been provided.
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Jan Springer earned 500 total points
ID: 40492712
NAT rules are processed in order.  Can you place this rule above your current NAT rule?

nat (outside,outside) source static REMOTE_IP NEW_PUBLIC destination static NEW_PUBLIC CURRENT_PUBLIC

nat(outside,outside) source static CURRENT_PUBLIC NEW_PUBLIC destination static NEW_PUBLIC REMOTE_IP

or

nat(inside,outside) source status REMOTE_IP NEW_PUBLIC destination static NEW_PUBLIC INSIDE_IP

nat(outside,inside) source static INSIDE_IP NEW_PUBLIC destination static NEW_PUBLIC REMOTE_IP
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