Overlapping NAT Performance.

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Jul 13th, 2009
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We just purchased a new company and I have been tasked to provide a NAT solution, because we have overlapping networks. I have the solution figured out:


Dynamic NAT with the "match host" option and DNS to accomplish what we need to do.


The question I have is performance. I am not sure how heavy the hardware requirements will be for this. I understand that DNS doctoring will do packet rewrites (performance hit?) for DNS replies. We were thinking of putting in a 2821 or 3800 series router. Would a firewall have more horsepower to perform this function?


The device will be JUST doing nat and maybe some simple routing.


Is there a doc that shows the maximum number of NAT translations per device (per memory load?)?


I have a requirement for dynamic nat pools and the "match host" option. I do not want the configuration and maintenance of static NAT entries.


Would the router/ASA do the DNS doctoring in hardware or software?


Would the router/ASA do the normal NAT translations in hardware or software?


Would CEF work for the NAT translations or would it be process switched?


Thanks,


Bret

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sbilgi Fri, 07/17/2009 - 14:03
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Cisco IOS NAT supports Cisco Express Forwarding switching, fast switching, and process switching. Performance depends on several factors:

• The type of application and its type of traffic

• Whether IP addresses are embedded

• Exchange and inspection of multiple messages

• Source port required

• The number of translations

• Other applications running at the time

• The type of hardware and processor

For most applications, degradation of performance due to NAT should be negligible.


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