NAT64 Prefixes

The FW determines whether to perform the NAT64 function on an IPv6 packet by checking whether the IPv6 packet contains the NAT64 prefix.

NAT64 prefixes are classified into the following types:

• Well-known prefix

  64:FF9B::/96, which exists by default.

• Pre-defined prefix

  The prefix with the length 32, 40, 48, 56, 64 or 96.

  Where an IPv4 address is embedded in an IPv6 address depends on the length of the NAT64 prefix, as shown in Figure 1. In a NAT64 prefix, PL indicates the length of the prefix, suffix can be a random value (the FW does not process this field), and U is the reserved octet of which the value must be set to 0.

  Figure 1 Embedding IPv4 addresses in IPv6 Addresses
  
  
  • When the prefix is 32 bits long, the IPv4 address is embedded in bits 32 to 63.
  • When the prefix is 40 bits long, 24 bits of the IPv4 address are embedded in bits 40 to 63, and the remaining 8 bits in bits 72 to 79.
  • When the prefix is 48 bits long, 16 bits of the IPv4 address are embedded in bits 48 to 63, and the remaining 16 bits in bits 72 to 87.
  • When the prefix is 56 bits long, 8 bits of the IPv4 address are embedded in bits 56 to 63, and the remaining 24 bits in bits 72 to 95.
  • When the prefix is 64 bits long, the IPv4 address is embedded in bits 72 to 103.
  • When the prefix is 96 bits long, the IPv4 address is embedded in bits 96 to 127. Bits 64 to 71 must be set to 0.

If an IPv4 address is 192.168.0.1 and the NAT prefix is 3000::/64, then the IPv6 address mapped to the IPv4 address is 3000:0000:0000:0000:00C0:A800:0100:0000, which can be abbreviated to 3000::C0:A800:100:0.

When you configure the DNS64 device, ensure that the DNS64 device and the FW has the same content and length of the NAT64 prefix.