TMS zl Management and Configuration Guide ST.1.2.100916

5-7
Network Address Translation
NAT Operations
Note For the sake of simplicity, the explanations of destination NAT will refer to
public and private IP addresses. You might choose to apply NAT between two
network segments, neither of which you define as public or private. (Note also
that all IP addresses used in the examples, whether labelled “public” or
“private,” are technically private IP addresses. They are used only to illustrate
the examples.)
One-to-One Translation (IP Address Only)
With this type of destination NAT, all traffic destined to a certain public IP
address is translated to the same private destination IP address. For example,
for the public NAT IP address, 192.168.5.23, there is one private IP address,
10.1.1.13. In the IP-only type of destination NAT, the destination address is
translated, but the port numbers are not translated.
The TMS zl Module will perform this type of NAT if you specify one destination
address, one NAT address, and no NAT port.
The source and destination IP address (SA, DA) and port fields (SP, DP) in five
inbound IP packet headers are shown in Table 5-4. The translated fields are
shown with shading.
Table 5-4. IP Address Only Destination NAT
Many-to-One Translation (IP Address Only)
With this type of destination NAT, several public IP address are translated to
a single private destination IP address. For example, all traffic destined to the
public IP addresses 192.168.5.23, 192.168.5.24, and 192.168.5.25 is translated
to the same private destination IP addresses, 10.1.1.10. The port is not trans-
lated.
This type of NAT allows external devices to contact several different IP
addresses to access the same internal server.
Before NAT After NAT
SA
1
SP
1
DA
1
DP
1
SA
2
SP
2
DA
2
DP
2
172.16.122.63 50055 192.168.5.23 80 172.16.122.63 50055 10.1.1.12 80
10.1.5.48 50056 192.168.5.23 21 10.1.5.48 50056
10.1.1.12 21
10.100.148.77 50057 192.168.5.23 88 10.100.148.77 50057
10.1.1.12 88
172.20.222.8 50058 192.168.5.23 53 172.20.222.8 50058
10.1.1.12 53
172.20.121.75 50059 192.168.5.23 69 172.20.121.75 50059
10.1.1.12 69