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Network Address Translation

Chapter Description

Network address translation (NAT) is a function by which IP addresses within a packet are replaced with different IP addresses. This function is most commonly performed by either routers or firewalls. This sample chapter from Cisco Press focuses on NAT within routers.

Command Summary

Table 4-4 provides a list and description of the commands discussed in this chapter

Table 4-4 Command Summary



clear ip nat translations {* | [inside [tcp {inside [global-ip [global-port] local-ip [local-port]} | udp {inside[global-ip [global-port] local-ip [local-port]}] | [inside global-ip local-ip][outside local-ip global-ip]

Clears dynamic entries from the NAT table.

ip nat {inside | outside}

Designates the inside and outside interfaces; traffic originating from or destined for the interface is examined by the NAT.

ip nat inside destination list {access-list-number|name} pool name

Enables translation of inside destination addresses.

ip nat inside source {list {access-list-number|name} pool name [overload] | static local-ip global-ip}

Enables translation of inside source addresses.

ip nat outside source {list {access-list-number|name} pool name | static global-ip local-ip}

Enables translation of outside source addresses.

ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length} type {rotary | match-host}

Defines a pool of addresses to be used for address translation.

ip nat translation max-entries entries

Sets a limit on the number of entries allowed in the NAT table.

ip nat translation {timeout | udp-timeout | dns-timeout | tcp-timeout | finrst-timeout | icmp-timeout | syn-timeout | port-timeout{tcp | udp}} seconds

Changes the default period after which a dynamic entry is removed from the NAT table and the address is returned to the pool.

show ip nat statistics

Displays NAT statistics.

show ip nat translations [verbose]

Displays the NAT table.

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