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NO-PAT supports all IP packets.
PAT
PAT translates multiple IPv6 addresses to a single IPv4 address by mapping each IPv6 address and
port to the IPv4 address and a unique port. PAT supports the following packet types:
• TCP packets.
• UDP packets.
• ICMPv6 echo request and echo reply messages.
PAT supports port blocks for connection limit and user tracing. Port blocks are generated by dividing
the port range (1024 to 65535) by the port block size. Port block based PAT maps multiple IPv6
addresses to one IPv4 address and uses a port block for each IPv6 address.
Port block based PAT functions as follows:
1. When an IPv6 host first initiates a connection to the IPv4 network, it creates a mapping from the
host's IPv6 address to an IPv4 address and a port block.
2. It translates the IPv6 address to the IPv4 address, and the source ports to ports in the port block
for subsequent connections from the IPv6 host until the ports in the port block are exhausted.
NOTE:
If the port range cannot be divided by the port block size exactly, the remaining ports are not used fo
translation.
Prefix translation
NAT64 prefix translation
NAT64 prefix is an IPv6 address prefix used to construct an IPv6 address representing an IPv4 node
in an IPv6 network. The IPv6 hosts do not use a constructed IPv6 address as their real IP address.
The length of a NAT64 prefix can be 32, 40, 48, 56, 64, or 96.
As shown in Figure 156, the co
nstruction methods vary depending on the NAT64 prefix length. Bits
64 through 71 in the constructed IPv6 address are reserved bits and must always be zero.
• If the prefix length is 32, 64, or 96 bits, the IPv4 address contained in the IPv6 address will be
integral.
• If the prefix length is 40, 48, or 56 bits, the IPv4 address contained in the IPv6 address will be
divided into two parts by bits 64 through 71.
Figure 156 IPv6 address construction with NAT 64 prefix and IPv4 address
AFT uses a NAT64 prefix to perform the following translation:
• IPv4-to-IPv6 source address translation. AFT translates a source IPv4 address to an IPv6
address that is created by using the NAT64 prefix and the IPv4 address.
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