Proxy

Protocol translation involves converting IPv4 packets into IPv6 packets and IPv6 packets into IPv4 packets. This translation typically involves some form of network address translation (NAT) in addition to the protocol translation (PT) function. It might run in a specialized node between an IPv4 network and an IPv6 network, or it might run in the host that owns the IPv4 application.

Protocol Translation is useful when devices need to communicate but are not using the same protocol, allowing IPv6-only devices to communicate with IPv4-only devices. However, the following issues make a less-than ideal solution:

Protocol translation is not foolproof. It is difficult to determine how long to keep the mappings between the real IPv6 address and the locally mapped IPv4 address available. An address can be reused before all servers have stopped accessing the address.
Some applications might use the remote IP address as a means of performing a security check. Unless AH or an IPSec tunnel is used, then this method is not foolproof, but it is still done. If the IPv4 address is a locally mapped address, any checks such as this are broken.
Displays and traces of the remote IP address are meaningless. Today, many applications generate messages, traces, and so on containing the IP address of the remote client.
All DNS queries for the IPv4-mapped address must flow through the node that performed the NAT function. The DNS resolver or name server at this node, as well as the TCP/IP stack, must maintain a mapping between the IPv4 address and IPv6 address.
Not all IPv6 protocols have IPv4 equivalents and not all IPv4 protocols have IPv6 equivalents. It might not be possible to translate the contents of an IPv4 packet into an equivalent IPv6 packet or the contents of an IPv6 packet into an equivalent IPv4 packet.