NAT performance

[jeffrey.zhou]

Although in the Cisco document, the NAT session limit is bounded by the amount of available DRAM in the router. But I found large number of NAT sessions will cause high CPU utilization. In Cisco 7206 NPE 200, when the NAT sessions reach 12000 entries, the CPU will be up to 99%. In Cisco 7206VXR NSE-1, When the number of NAT sessions reach 19000, the CPU utilization will be up to 95%. In these cases, the router CPU reach its limit prior to the memory reaching its limit. So is it normal in above cases?

[rsissons]

The CPU usage will depend on the number os frames that are being passed on each NAT session, rather than just the number of NAT sessions that have been established so, if your NAT sessions are very busy this will invlve a high CPU overhead.

[jeffrey.zhou]

But are there any figures that can be used as reference to justify if the router is in the normal status. For example, under some pre-defined conditions and on some platforms, how many active NAT translation sessions and how many pps can be supported. We have been challenged by the customer that there is no significant improvement between a NPE 200 and NSE-1.