Overlapping NAT Performance.

Unanswered Question
Jul 13th, 2009

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

I have this problem too.
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sbilgi Fri, 07/17/2009 - 14:03

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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