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ASA 5505 Config question

Posted on 2011-02-17
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Last Modified: 2012-05-11
Hello all...

I am fairly new to ASA configurations... but I had a question.

In a config setup of:

hostname(config)# object network my-host-obj1
hostname(config-network-object)# host 1.1.1.1
hostname(config-network-object)# nat (inside,outside) static 2.2.2.2 dns

What exactly does the 'dns' do on line 3 exactly?  If I just want to setup a static route, it works without it, but what does it do, and do you want it or not?

Thanks
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Question by:Bryan_
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by:
MikeKane earned 250 total points
ID: 34919441
Taken right from the command reference:
dns
      (Optional) Translates DNS replies. Be sure DNS inspection (inspect dns) is enabled (it is enabled by default). This option is not available if you specify the service keyword (for static NAT). For more information, see the Cisco ASA 5500 Series Configuration Guide using the CLI.


In English:
If this internal IP makes dns replies, the ASA will rewrite the outbound packet to reflect the public ip in the translation rule.
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Assisted Solution

by:Kvistofta
Kvistofta earned 250 total points
ID: 34919478
No. Not "if this internal ip"... If ANYONE on inside makes ANY DNS-request and the reply contains the global IP (2.2.2.2), the dns-reply will be rewritten to contain "1.1.1.1" instad of "2.2.2.2".

Best regards
Kvistofta
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Author Comment

by:Bryan_
ID: 34921000
Thank you.

So for a web server to be used on that configuration, you would want the 'dns' set in that command.

Any reason to not do it?
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Expert Comment

by:MikeKane
ID: 34921554
I run split dns, so i don't really need this.    My internal dns handles internal resolution.   My external dns for people outside, would give them the correct public IP.
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Author Closing Comment

by:Bryan_
ID: 34921634
Thanks for the clear and quick replies!!!
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