H3C Technologies H3C SecPath F1000-E - Manual (Page 188)

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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.
Session initiated by an IPv4 host
The NAT-PT implementation process for a session initiated by an IPv4 host is as follows:
1. Determines whether to perform NAT-PT or not
Upon receiving a packet from an IPv4 host to an IPv6 host, the NAT-PT device checks the destination IPv4
address in the packet against the static mappings configured on the IPv6 network side. If a match is
found, the device considers that the packet needs to be forwarded to the IPv6 network and NAT-PT needs
to be performed.
2. Translates the source IP address
The NAT-PT device translates the source IPv4 address of the packet into an IPv6 address according to the
static or dynamic mapping on the IPv4 side. If no mapping is configured on the IPv4 side, the source IPv4
address with the first configured NAT-PT prefix is used as the translated source IPv6 address.
3. Translates the destination IP address
The NAT-PT device translates the destination IPv4 address of the packet into an IPv6 address according
to the static mapping on the IPv6 side.
4. Forwards the packet and stores the mappings
After the source and destination IPv4 addresses of the packet are translated into IPv6 addresses, the
NAT-PT device forwards the packet to the IPv6 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 IPv6 host to the IPv4 host, the NAT-PT device swaps the source
and destination IPv6 addresses according to the stored mappings and forwards the packet to the IPv4
host.
NAT-PT Limitations
NAT-PT has the following limitations:
• In NAT-PT translation, the request and response packets of a session must be processed by the same
NAT-PT device.
• The Options field in the IPv4 packet header cannot be translated.
• NAT-PT does not provide end-to-end security.
Therefore, NAT-PT is not recommended in some applications. For example, tunneling is recommended in
the case where an IPv6 host needs to communicate with another IPv6 host across an IPv4 network.