How Nat Works; Port Restricted Cone Nat; Figure 34 How Nat Works - Nortel BSR222 Configuration

Chapter 8 Network Address Translation (NAT) Screens 133

How NAT works

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 (local) IP addresses to
globally unique ones required for communication with hosts on other networks. It
replaces the original IP source address (and TCP or UDP source port numbers for
Many-to-One and Many-to-Many Overload NAT mapping) in each packet and
then forwards it to the Internet. The Business Secure Router keeps track of the
original addresses and port numbers so incoming reply packets can have their
original values restored, as illustrated in Figure 34.

Figure 34 How NAT works

Business Secure Router

Port Restricted Cone NAT

The Business Secure Router uses port restricted cone NAT.
Port restricted cone NAT maps all requests from the same private IP address and
port to the same public IP address and port. A host on the Internet can only send a
packet to the private IP address and port if the private IP address and port has
previously sent a packet to that host's IP address and port.
Nortel Business Secure Router 222 Configuration — Basics