ZyXEL Communications Prestige 2002 - Manual (Page 49)

P-2002 Series User’s Guide
Chapter 5 Introduction to VoIP 49
NAT may be implemented on a device that is between your Prestige and the Internet.
5.3.1 NAT Example
See the following figure. The Prestige (X) sends packets to the Internet. The Prestige’s IP
address is 10.0.0.3. This is a private or internal IP address. The NAT router maps the private
source IP address to a public source IP address (a.b.c.d). The public source IP address is also
known as the external IP address.
Note: The NAT figures in this chapter use lower-case letters (like a.b.c.d for example)
to represent public IP addresses.
Figure 17 NAT: Outgoing
When the NAT router receives packets with destination address IP address a.b.c.d, the NAT
router changes a.b.c.d back to the private IP address 10.0.0.3 and sends it to the Prestige.
Figure 18 NAT: Incoming
5.3.2 NAT Types
This section discusses the following NAT types that may be implemented on a router in front
of the Prestige.
• Full Cone
• Restricted Cone
• Port Restricted Cone
• Symmetric