ZyXEL Communications AMG1302-T11C - 11.6 NAT Technical Reference

Chapter 11 Network Address Translation (NAT)
AMG1302-T11C User’s Guide
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The following table describes the labels in this screen.
11.6 NAT Technical Reference
This chapter contains more information regarding NAT.
11.6.1 NAT Definitions
Inside/outside denotes where a host is located relative to the AMG1302-T11C, 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.
NAT never changes the IP address (either local or global) of an outside host.
11.6.2 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.
Table 54 Network Setting > NAT > ALG
LABEL DESCRIPTION
ALG Enable this to make sure SIP (VoIP) works correctly with port-forwarding and address-
mapping rules.
Apply Click this to save your changes.
Cancel Click this to restore your previously saved settings.
Table 55 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.