H3C S9500 Series Operation Manual page 126

Operation Manual – NAT
H3C S9500 Series Routing Switches
Packets 1 and 2 are from the same internal address but have different source port
numbers.
Packets 3 and 4 are from different internal addresses but have the same source
port number.
By using NAPT mapping, the four packets are translated into the same public address,
but are given different source port numbers. In this way, the differences between the
four packets are kept, and the NAT process can distinguish the response packets for
each of them by destination address and port number.
III. Easy IP
With the nat outbound command configured, NAT with the Easy IP feature uses the
public address of the VLAN interface on the NAT equipment as the translated source
addresses. If you have only one public network IP address available or you have a
limited number of internal IP addresses to be translated, you can use Easy IP to
implement NAT.
IV. Internal Servers
NAT conceals the internal network topology and acts as a shield for internal hosts. But
in practical applications, it might be required to provide some chances for external
hosts to access certain internal devices such as internal WWW servers or FTP servers.
By using NAT, you can flexibly add internal servers. For instance, you can use
202.169.10.10 as the public address for an internal WWW server, and 202.110.10.11
as that for an FTP server. You can even use 202.110.10.12:8080 as the public address
for an internal WWW server.
If a user is not concerned about (or does not know) the port number of an internal server,
you can configure the NAT AnyServer function to simplify internal server configuration.
The AnyServer feature allows a public host to access all the ports of a specific protocol
(ICMP provides no port information) on an internal server and thus hosts on the public
network and private network can access each other. For example, a public host can use
the public IP address 202.168.20.10 of an internal server to access all TCP ports on the
internal server, or use the public IP address 202.168.20.11 of another internal server to
access all UDP ports on it.
V. Static NAT
You can map the IP address of an internal host to a fixed public address through static
NAT. For example, you can map the IP address 192.168.30.10 of an internal host to
public address 202.168.30.10. Then, if the host sends packets to the public network,
the source IP address in the packets will be translated to 202.168.30.10; the external
hosts can also access the internal host directly using the public address 202.168.30.10.
Comparison between AnyServer and static NAT:
1-5
Chapter 1 NAT Configuration