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Cisco ASA Series Firewall CLI Configuration Guide
 
Chapter 9      Network Address Translation (NAT)
  History for NAT
Per-session PAT 9.0(1) The per-session PAT feature improves the scalability of PAT 
and, for clustering, allows each member unit to own PAT 
connections; multi-session PAT connections have to be 
forwarded to and owned by the master unit. At the end of a 
per-session PAT session, the ASA sends a reset and 
immediately removes the xlate. This reset causes the end 
node to immediately release the connection, avoiding the 
TIME_WAIT state. Multi-session PAT, on the other hand, 
uses the PAT timeout, by default 30 seconds. For 
“hit-and-run” traffic, such as HTTP or HTTPS, the 
per-session feature can dramatically increase the 
connection rate supported by one address. Without the 
per-session feature, the maximum connection rate for one 
address for an IP protocol is approximately 2000 per 
second. With the per-session feature, the connection rate for 
one address for an IP protocol is 65535/average-lifetime.
By default, all TCP traffic and UDP DNS traffic use a 
per-session PAT xlate. For traffic that requires multi-session 
PAT, such as H.323, SIP, or Skinny, you can disable 
per-session PAT by creating a per-session deny rule.
We introduced the following commands: xlate per-session, 
show nat pool.
Transactional Commit Model on NAT Rule 
Engine
9.3(1) When enabled, a NAT rule update is applied after the rule 
compilation is completed; without affecting the rule 
matching performance.
We added the nat keyword to the following commands: asp 
rule-engine transactional-commit, show running-config 
asp rule-engine transactional-commit, clear configure 
asp rule-engine transactional-commit.
 to 
Feature Name
Platform 
Releases Description