TMS zl Management and Configuration Guide ST.1.0.090213

5-4
Network Address Translation
NAT Operations
Figure 5-1. Source NAT
Note Source NAT is often referred to as just NAT. This guide will always refer to it
as source NAT.
One-to-One
With one-to-one source NAT, each local device receives its own new IP address
for the destination network. The source IP address is replaced with the NAT
IP address, but the source port remains the same. The TMS zl Module will
perform one-to-one NAT if the number of source addresses and the number
of NAT addresses is identical.
The source and destination IP address (SA, DA) and port fields (SP, DP) in five
outbound IP packet headers are shown in Table 5-1. The translated fields are
shown with shading.
Table 5-1. One-to-One Source NAT
Many-to-One
With many-to-one source NAT, many local devices share the same IP address
in the destination network. That is, the module translates each source IP
address to the same new IP address. However, each local device retains its
own source port. Return traffic to the local devices is all destined to the same
IP address but to different ports. Thus the module can forward return traffic
to the correct device. The TMS zl Module will perform many-to-one NAT if you
specify multiple source addresses and one NAT address.
This is the most commonly used type of source NAT.
Before NAT After NAT
SA
1
SP
1
DA
1
DP
1
SA
2
SP
2
DA
2
DP
2
10.1.1.10 50055 172.16.122.63 80 192.168.5.21 50055 172.16.122.63 80
10.1.1.11 50056 192.168.2.77 21
192.168.5.22 50056 192.168.2.77 21
10.1.1.12 50057 172.16.222.8 88
192.168.5.23 50057 172.16.222.8 88
10.1.1.13 50058 192.168.2.75 53
192.168.5.24 50058 192.168.2.75 53
10.1.1.14 50059 172.16.53.78 69
192.168.5.25 50059 172.16.53.78 69