from probing your network. For more information on IP address translation, refer to RFC 1631, The IP Network Address Translator (NAT).
Inside/outside indicates where a host is located relative to the ROUTER. The computers hosts of your LAN are inside, while the Web servers on the Internet are outside.
Global/local indicates the IP address of a host in a packet as the packet traverses a router. The local address refers to the IP address of a host when the packet is in the local network, while the global address refers to the IP address of the host when the same packet is traveling in the WAN side.
Note that inside/outside refers to the location of a host, while global/local refers to the IP address of a host used in a packet. Thus, an inside local address (ILA) is the IP address of an inside host of a packet when the packet is still in the local network, while an inside global address (IGA) is the IP address of the same inside host when the packet is on the WAN side.
The following table summarizes this information.
| ITEM | DESCRIPTION |
|
Inside | This refers to the host on the LAN. | |
|
|
|
Outside | This refers to the host on the WAN. | |
|
|
|
Local | This refers to the packet address (source or destination) as the | |
| packet travels on the LAN. | |
|
|
|
Global | This refers to the packet address (source or destination) as the | |
| packet travels on the WAN. | |
|
|
|
Each packet has two addresses – a source address and a destination address. For outgoing packets, the ILA is the source address on the LAN, and the IGA is the source address on the WAN. For incoming packets, the ILA is the destination address on the LAN, and the IGA is the destination address on the WAN. NAT maps private (local) IP addresses to globally unique ones required for communication with hosts on other networks. It replaces the original IP source address (and TCP or UDP source port numbers for
The following figure illustrates this.
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