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NE20E-S2 V800R010C10SPC500 Feature Description - NAT and IPv6 Transition 01

This is NE20E-S2 V800R010C10SPC500 Feature Description - NAT and IPv6 Transition
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NAT Classification

NAT Classification

NAT translates between private and public IP addresses carried in the headers of IP data packets. Two modes are available: Port Address Translation (PAT) and no-PAT.

PAT-based NAT Translation

PAT-based NAT translation is also called network address port translation (NAPT). NAPT translates both source IP addresses and port numbers between public and private networks. For packets with the same private source IP addresses and different source port numbers, NAPT translates the private source IP address in each packet to the same public source IP address and each private source port number to a specific public source port number.

Figure 2-1 PAT-based NAT translation
In Figure 2-1, a NAT device receives three packets. Packet 1 and packet 2 carry the same private source IP address but different source port numbers. Packet 1 and packet 3 carry different private source IP addresses but the same source port number. The NAT device uses NAPT to translate the private source IP addresses into the same public source IP address and each private source port number into a specific public source port number. After the NAT device receives the response packet to each packet, the NAT device can distinguish these packets and properly send them to hosts on the private network.

In NAPT mode, when a NAT device converts both IP addresses and port numbers in packets. The NATP mode more efficiently uses IP address resources to allow more internal hosts to access the internet. In addition, the NATP mode supports fragments. When basic NAT is used, each private IP address is mapped to a public IP address, which wastes IP address resources. Therefore, the NAPT mode is recommended.

No-PAT-based NAT Translation

No-PAT only translates each private source IP address into a public source IP address, but does not translate source port numbers.

Figure 2-2 No-PAT-based NAT translation

In Figure 2-2, two packets carrying private IP addresses arrive at a NAT device. Packet 1 and packet 2 carry different private source IP addresses and port numbers. The no-PAT mapping is used to convert the source IP addresses in the two data packets to different two public IP addresses, with source interfce numbers unchanged.

No-PAT is used by enterprises for services with high privacy. For example, customers in financial industry require not to show the private IP addresses carried in service packets transmitted over a public network. In addition, some financial applications use the fixed port numbers, and No-PAT can meet such a requirement.

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Updated: 2019-01-02

Document ID: EDOC1100055472

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