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This section discusses NAT verification commands on a Cisco IOS router. You can display translation information and clear address translation entries from the NAT translation with the commands covered in this section.
The show ip nat translations command can be used to verify the active translations. The screen
outputs can be seen in the following examples.
Example
shows a basic translation.
Example
is a sample of NAT with overloading. Two different inside hosts appear on the outside with a single IP address, both for a
Telnet session—destination TCP port 23. Unique source TCP port
numbers are used to distinguish between the hosts.
You can use the
show ip nat statistics
command to see NAT statistics.
Dynamic NAT Timeouts
By default, dynamic address translations time out after some period of
nonuse. You can change the default values on timeouts, if necessary. When overloading is not configured, simple translation entries time out after 24 hours.
If you have configured overloading, you have finer control over the translation entry timeout because each entry contains more context about the traffic that is using it. The following are the timeout values with NAT overloading:
UDP timeout value: 5 minutes
DNS timeout value: 1 minute
TCP timeout value: 24 hours
Finish and Reset value: 1 minute
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