Can Cisco resolve internet address internally

jgrammer42
jgrammer42 used Ask the Experts™
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Here is the situation.  I have an internet domain of CORPORATION.COM

Exchange is the mail server with the DNS name of MAIL.CORPORATION.COM on the internet.

MAIL.CORPORATION.COM is used by laptop, (for example), for Outlook Anywhere access.

MAIL.CORPORATION.COM resolves to internet address of 200.250.192.100  (again, just an example)

My Cisco ASA NAT's the external IP of 200.250.192.100 to the internal LAN address of 192.168.1.50

All of that works great.  No problems.

However, when someone with a laptop comes into the corporate office, and tries to resolve the name of MAIL.CORPORATION.COM,  the internet DNS responds with 200.250.192.100 which the Cisco is unable to resolve or map back to the internal network of 192.168.1.50, which is the Cisco's internal known IP network.

For years, the way around this is to set up on the INTERNAL LAN DNS a CORPORATION.COM domain, that all local LAN clients would use to resolve back to the internal LAN network of 192.168.1.y, instead of to an external Internet address.

Frankly, I HATE that solution.  I always thought it was kludgy at best.

So, the question is this, is there a way to configure the Cisco that if it sees an internet address that maps to its known internal LAN network IP, it will automatically respond back with that internal LAN address instead of just getting stuck in a loop?

Thank you in advance,
Jeff
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Top Expert 2014

Commented:
In my opinion, a split DNS really is the best way to handle things like this (not sure why you would consider it kludgy).  If you only have one or a few resources that should resolve to a different IP depending on whether the client is on the internal network or coming over the internet, then you can create specific zones for those resources rather than creating one zone to cover all of CORPORATION.COM.  For example, you would create a zone for MAIL.CORPORATION.COM and then create an A record in it with a blank name which points to the internal IP.  This leaves other queries for records in the CORPORATION.COM domain (anything not like xxx.MAIL.CORPORATION.COM) free to be resolved by records on the public DNS.

I've no clue whether your Cisco could do what you ask, but I would be quite surprised if it could.
Top Expert 2014
Commented:
You can do DNS rewrite (commonly called doctoring) at the ASA...

https://supportforums.cisco.com/document/145401/dns-doctoring-and-u-turning-asa-when-and-how-use-it

Author

Commented:
Hi Craig,
This appears to be exactly what I was looking for.  I will test this out this weekend and see how it works.

Thank you,
Jeff

Author

Commented:
thank you

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