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S9700 Core Routing Switch
Configuration Guide - SPU
Figure 3-2 PAT working process
Internal Server
NAT can shield internal hosts. In applications, users on the public network may need to access
the internal hosts. For example, users on the public network need to access a Web server or a
file transfer protocol (FTP) server.
NAT allows you to flexibly configure IP addresses for internal servers. For example, you can
use 202.110.10.10 or even 202.110.10.12:8080 as the public address of a Web server, and use
202.110.10.11 as the public address of an FTP server. Multiple servers (Web servers for
example) can be provided for external user.
You can configure an internal server and map the public address and port to the internal server.
In this way, hosts on the public network can access the internal server.
NAT Mapping
The NAT function saves IPv4 addresses and improves network security. NAT implementation
of different vendors may be different; therefore, the applications using the simple traversal of
UDP through NAT (STUN), traversal using relay NAT (TURN), and Interactive Connectivity
Establishment (ICE) technologies may fail to traverse the NAT devices of these vendors. These
technologies are commonly used on the SIP proxy. NAT mapping enables these applications to
traverse the NAT devices.
NAT Filtering
A NAT device filters the traffic from external network to internal network. After a host on the
internal network sends an access request to a host on the external network, the host on the external
Issue 01 (2012-03-15)
Datagram 1
Src IP: 192.168.1.3
Src Port:23
Datagram 2
Src IP: 192.168.1.3
Src Port:80
192.168.1.3
192.168.1.2
Datagram 3
Src IP: 192.168.1.2
Src Port:23
Datagram 4
Src IP: 192.168.1.2
Src Port:80
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Datagram 1
Src IP: 202.169.10.1
Src Port:10023
Datagram 2
Src IP: 202.169.10.1
Src Port:10080
SPU
Datagram 3
Src IP: 202.169.10.1
Src Port:11023
Datagram 4
Src IP: 202.169.10.1
Src Port:11080
3 NAT Configuration
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