Billion Electric Company 5100S User Manual

 

35

This chapter discusses how to configure NAT on the BIPAC 5100S.

 

NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a 

host in a packet, for example, the source address of an outgoing packet, used within one 

network to a different IP address known within another network. 

Inside/outside denotes where a host is located relative to the BIPAC 5100S, for example, the 

computers of your subscribers are the inside hosts, while the web servers on the Internet are 

the outside hosts. 

Global/local denotes the IP address of a host in a packet as the packet traverses a router, for 

example, 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 in 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. 

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. 

In the simplest form, NAT changes the source IP address in a packet received from a 

subscriber (the inside local address) to another (the inside global address) before forwarding 

the packet to the WAN side. When the response comes back, NAT translates the destination