R3303-HP HSR6800 Routers Layer 3 - IP Services Configuration Guide

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NAT-PT prefix
The 96-bit NAT-PT prefix in the IPv6 address prefix format is used in the following cases:
• Upon receiving a packet from an IPv6 host to an IPv4 host, the NAT-PT device detects the prefix of
the destination IPv6 address in the packet. If the prefix is the same as the configured NAT-PT prefix,
the device translates source and destination IPv6 addresses of the packet into IPv4 addresses.
• After a packet from an IPv4 host to an IPv6 host is translated through NAT-PT, the prefix of the
translated source IPv6 address is the configured NAT-PT prefix.
Implementing NAT-PT
Session initiated by an IPv6 host
Figure 82 NAT-PT implementation (session initiated by an IPv6 host)
NAT-PT works as follows:
1. Determines whether to perform NAT-PT.
Upon receiving a packet from an IPv6 host to an IPv4 host, the NAT-PT device detects the prefix of
the destination IPv6 address in the packet. If the prefix is the same as the configured NAT-PT prefix,
the device considers that the packet needs to be forwarded to the IPv4 network and NAT-PT needs
to be performed.
2. Translates the source IP address.
The NAT-PT device translates the source IPv6 address of the packet into an IPv4 address according
to the static or dynamic mapping on the IPv6 side.
3. Translates the destination IP address.
The NAT-PT device translates the destination IPv6 address of the packet into an IPv4 address
according to the static mapping, if configured, on the IPv4 network side. Without any static
mapping configured on the IPv4 network side, if the lowest 32 bits of the destination IPv6 address
in the packet can be directly translated into a valid IPv4 address, the destination IPv6 address is
translated into that IPv4 address. Otherwise, the translation fails.
4. Forwards the packet and stores the mappings.
After the source and destination IPv6 addresses of the packet are translated into IPv4 addresses,
the NAT-PT device forwards the packet to the IPv4 host. Meanwhile, the IPv4/IPv6 address
mappings are stored in the NAT-PT device.
5. Forwards the reply packet according to the stored mappings.
Upon receiving a reply packet from the IPv4 host to the IPv6 host, the NAT-PT device swaps the
source and destination IPv4 addresses according to the stored mappings and forwards the packet
to the IPv6 host.