Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Overlapping NAT Performance.

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?



  • Getting Started with LANs

Re: Overlapping NAT Performance.

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.

This widget could not be displayed.