Configuring NAT

Before the use of any device we have to configure it or either we should get familiar with the knowhow of that device. Our today`s article is related to the configuration of NAT (Network Address Translation). NAT (Network Address Translation) replaces IP addresses within a packet with different IP addresses. Nat is very useful in many circumstances such as:

•    Conserving IP address space.
•    Implementing TCP load distribution.
•    Connection networks with overlapping addresses.
•    During network migration, this involves the renumbering of nodes.
•    Connecting a private network using an unregistered address to a public network like the internet.
•    Distributing other Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)
Based (UDP) based services.

A router configured for NAT maintains a translation table that has the mapping between the addresses used in the translation.
Configuring NAT involves identifying the NAT inside and NAT outside interfaces, then configuring the way the addresses are to be translated, depending on the requirement.

A router configured with NAT translates only traffic that is forwarded between the inside and outside interfaces, and the flow that matches the criteria specified for translation.

Traffic that does not meet these conditions is forwarded without any translation.

A static NAT configuration creates a one-to-one mapping and translates a specific address to another address.

This type of configuration creates a permanent entry in the NAT table, as long as the configuration is present and is useful when users on both inside and outside networks need to initiate a connection.

To configure static NAT, issue the IP Nat inside source static or IP Nat outside source static commands in global configuration mode, depending on where the host is located.

Static NAT can also be used to redirect traffic using a particular port to a different port on a host.

This is helpful when the users belonging to the inside network use a particular port number to access a particular application (like a web server) available on the inside or outside network.

The same application is accessed by users from the outside network using a different port number.

To redirect traffic to a different port, issue the IP Nat inside source {static {tcp|udp local-ip local-port global-ip global-port} [extendable] or ip nat outside source {static tcp|udp global-ip global-port local-i`p local-port} [extendable] commands in global configuration mode, depending on whether the inside or outside network is available.

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