Operation Manual – NAT, Netstream, Policy RoutingH3C S7500 Series Ethernet Switches Chapter 1 NAT Configuration1-1Chapter 1 NAT ConfigurationWhen configuring NAT, go to these sections for information you are interested in:z NAT Overviewz NAT Featuresz Configuring NATz Displaying NAT Configurationz NAT Configuration ExampleNote:Currently, the LS81VSNP boards installed in S7500 series switches support the NATfeature. In this manual, the LS81VSNP board is called LPU (line processing unit).1.1 NAT OverviewAs described in RFC1631, network address translation (NAT) is a procedure totranslate the private IP address in packet header into a public IP address. With NAT, aprivate network that provides a great number of private addresses for its internal usersto communicate with each other can use relatively smaller quantity of public addressesfor its internal users to access the Internet. This allows private network users to accesspublic networks and saves public IP address resources.Note:Private IP addresses refer to the addresses used by the hosts in a private network tocommunicate to each other instead of to external networks. Public IP addresses referto the globally unique, registered IP addresses that can be used on the Internet.RFC1918 reserves the following three blocks of IP addresses for private networks:z Class A: from 10.0.0.0 to 10.255.255.255z Class B: from 172.16.0.0 to 172.31.255.255z Class C: from 192.168.0.0 to 192.168.255.255The above three blocks of IP addresses are not for use on the Internet, and users canuse them freely within their enterprises without the necessary to apply to the ISP or NICfor them.The following figure depicts a basic NAT application.
