LTE TDD B2268H
User Guide
8 Network Address Translation (NAT)
Issue 01 (2014-01-15)
Copyright © Huawei Technologies Co., Ltd.
72
8.6.1 NAT Definitions
Inside/outside denotes where a host is located relative to the LTE Device, 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.
Table 8-5
NAT Definitions
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.
NAT never changes the IP address (either local or global) of an outside host.
8.6.2 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) back 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. If you do not define any
servers, NAT offers the additional benefit of firewall protection. With no servers defined, your
LTE Device filters out all incoming inquiries, thus preventing intruders from probing your
network. For more information on IP address translation, refer to
RFC 1631
,
The IP Network
Address Translator (NAT)
.
8.6.3 How NAT Works[h1]
Each packet has two addresses-a source address and a destination address. For outgoing packets,
the ILA (Inside Local Address) is the source address on the LAN, and the IGA (Inside Global
Address) 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
