Solved: IOS NAT - how long do NAT translations live?

mmedwid · ‎08-28-2008

When I run a "show ip nat translations" I get a table of traffic that's been NATTED and to where that traffic was headed. The question I have is - how long do these translations live before they expire?

tdrais · ‎08-28-2008

Only active ones.

If you look in the note is says TCP sessions that see a FIN or RST are 1 minute. So if they are closed they will be cleared in 1 minute.

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tdrais · ‎08-28-2008

1-5 minutes unless you change them.

http://www.cisco.com/en/US/docs/ios/ipaddr/command/reference/iad_nat.html#wp1013201

mmedwid · ‎08-28-2008

It looks like TCP is actually set to default to 24 hours:

http://www.ciscopress.com/articles/article.asp?p=25273&seqNum=5

..and your article confirms that.

I found the verbose switch on the command "show ip nat trans" and that confirmed the 24 hours of persistence in the table.

tdrais · ‎08-28-2008

Only active ones.

If you look in the note is says TCP sessions that see a FIN or RST are 1 minute. So if they are closed they will be cleared in 1 minute.

mmedwid · ‎08-28-2008

Thank-you - great point.