Cisco Systems 78-11741-02 Changing Translation Timeouts, Translations that do not use overloading

Configuring IP Addressing

Configuring Network Address Translation

	Command		Purpose
Step 1
	Router(config)# ip	nat pool name start-ip end-ip	Defines a pool of addresses containing the addresses
	{netmask netmask prefix-length prefix-length}type		of the real hosts.
	rotary
Step 2
	Router(config)# access-listaccess-list-number		Defines an access list permitting the address of the
	permit source [source-wildcard]		virtual host.
Step 3
	Router(config)# ip	nat inside destination list	Establishes dynamic inside destination translation,
	access-list-number	pool name	specifying the access list defined in the prior step.
Step 4
	Router(config)# interface type number		Specifies the inside interface.
Step 5
	Router(config-if)#	ip nat inside	Marks the interface as connected to the inside.
Step 6
	Router(config)# interface type number		Specifies the outside interface.
Step 7
	Router(config-if)#	ip nat outside	Marks the interface as connected to the outside.

Note The access list must permit only those addresses that are to be translated. (Remember that there is an implicit “deny all” at the end of each access list.) An access list that is too permissive can lead to unpredictable results.

See the “ping Command Example” section at the end of this chapter for an example of rotary translation.

Changing Translation 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. To change this value, use the following command in global configuration mode:

Command	Purpose
Router(config)# ip nat translation timeout seconds	Changes the timeout value for dynamic address
	translations that do not use overloading.

If you have configured overloading, you have more control over translation entry timeout, because each entry contains more context about the traffic using it. To change timeouts on extended entries, use the following commands in global configuration mode as needed:

Command	Purpose
Router(config)# ip nat translation udp-timeout seconds	Changes the UDP timeout value from 5 minutes.
Router(config)# ip nat translation dns-timeout seconds	Changes the DNS timeout value from 1 minute.
Router(config)# ip nat translation tcp-timeout seconds	Changes the TCP timeout value from 24 hours.
Router(config)# ip nat translation finrst-timeout seconds	Changes the Finish and Reset timeout value from
	1 minute.

Cisco IOS IP Configuration Guide

IPC-45