Nat Features Supported By The Spu - Huawei S9700 Series Configuration Manual

S9700 Core Routing Switch
Configuration Guide - SPU
The host sends a data packet, and uses port 6084 as the source port and port 80 as the destination
port. After the address is translated, the source address/port of the packet is changed to
203.196.3.23:32814, and the destination address/port remains unchanged. The SPU maintains
a mapping table between addresses and ports.
After the web server responds to the host, the SPU translates the destination IP address/port in
the returned data packet to 10.1.1.48:6084. In this way, the host on the private network can access
the server on the public network.

3.2 NAT Features Supported by the SPU

The SPU supports the following NAT features: static NAT, port address translation (PAT),
internal server, NAT Application Level Gateway (ALG), NAT filtering, NAT mapping, Easy
IP, twice NAT, and NAT multi-instance.
Static NAT
Static NAT maps a private address to a public address. That is, the number of private addresses
is equal to the number of public addresses. Static NAT cannot save public addresses, but can
shield the topology of the private network.
When a packet is sent from a private network to the public network, static NAT translates the
source IP address of the packet to a public address. When the public network returns a response,
static NAT translates the destination IP address of the response packet to the private address.
PAT
Port address translation (PAT), which is also called network address port translation (NAPT),
maps a public address to multiple private addresses. Therefore, public addresses are saved. PAT
translates source IP addresses of packets from hosts that reside on the private network to a public
address. The translated port numbers of these packets are different, and the private addresses
can share a public address.
A mapping table between private addresses and ports is configured for PAT. Before packets
from different private addresses are sent to the public network, the PAT-enabled device replaces
the source addresses with the same public address. The source port numbers of the packets,
however, are replaced with different port numbers. When the public network returns response
packets to private networks, the PAT-enabled device translates the destination IP addresses to
private addresses according to the port numbers.
addresses and port numbers.
Issue 01 (2012-03-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
Figure 3-2 shows how PAT translates IP
3 NAT Configuration
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