What Nat Does; Table 23 Nat Definitions - Nortel BSR252 Configuration - Basics

130 Chapter 8 Network Address Translation (NAT) Screens
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.

Table 23 NAT definitions

Term
Inside
Outside
Local
Global

What NAT does

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 address (the inside global address) to the inside
local address before forwarding it to the original inside host. Note that the IP
address (either local or global) of an outside host is never changed.
The global IP addresses for the inside hosts can be either static or dynamically
assigned by the ISP. In addition, you can designate servers (for example a web
server and a Telnet server) on your local network and make them accessible to the
outside world. You can make designated servers on the LAN accessible to the
outside world. If you do not define any servers (for Many-to-One and
Many-to-Many Overload mapping), NAT offers the additional benefit of firewall
protection. With no servers defined, your Business Secure Router filters out all
incoming inquiries, thus preventing intruders from probing your network. For
more information about IP address translation, refer to The IP Network Address
Translator (NAT) (RFC 1631).
NN47923-500
Description
This refers to the host on the LAN.
This refers to the host on the WAN.
This refers to the packet address (source or destination) as the packet
travels on the LAN.
This refers to the packet address (source or destination) as the packet
travels on the WAN.
Note: NAT never changes the IP address (either local or global) of an
outside host.
Table 23 summarizes this information.