Cisco IOS NAT supports Cisco Express Forwarding switching, fast switching, and process switching. For 12.4T release and later, fast-switching path is no longer supported. For Cat6k platform, the switching order is Netflow (HW switching path), CEF, process path.
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