Datatek IPv6 Transformer User Manual - Manual (Page 13)

S E C T I O N 2 O V E R V I E W
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2 Overview
Throughout this document, the following definitions and conventions will be used:
Host-side refers to the attachment point for the IPv4 legacy device. This is the physical connection
labeled IPv4 on the Transformer’s front panel. Network-side refers to the IPv6 or IPv4/IPv6 dual
network which is connected to a hub or router. This is the physical connection labeled IPv6 on
the Transformer’s front panel.
2.1 How the Transformer Works
The Transformer has two interfaces, the host-side and network-side interfaces. The legacy IPv4
device is connected to the Transformer on the host-side IPv4 interface while the IPv6 network is
connected on the network-side IPv6 interface. The Transformer receives IPv4 packets from the
legacy IPv4 device through the IPv4 interface and translates them into IPv6 packets to send out
the network-side interface. It receives IPv6 packets from the network-side interface and translates
them into IPv4 packets and sends them out the host-side interface. The Transformer uses a
mapping table that contains one-to-one bindings between surrogate IPv4 addresses and IPv6
addresses. The binding between the legacy IPv4 address and its proxy IPv6 address is automatic.
Other bindings are either configured manually using the
Static address map form or created
dynamically by the Transformer when it selects an available IPv4 address from the IPv4 address
pool that was configured on the
Address pool form.
The Transformer has IPv4 and IPv6 addresses assigned to represent itself to the world for
management purposes, but the Transformer also establishes public IPv4 and IPv6 addresses to
represent the host's private IPv4 address.
When the IPv4 host sends a packet to an IPv4 address on the network side, the Transformer
substitutes the host’s private IPv4 address with the public IPv4 address representing the host on
the Transformer, and then transmits that packet to the network. When the IPv4 host transmits a
packet to an IPv6 endpoint, its private IPv4 address is mapped to the public IPv6 address on the
Transformer, the surrogate destination IPv4 address is mapped to the actual IPv6 destination, and
protocol translation from IPv4 to IPv6 is performed. This packet is then routed to the network
IPv6 address.
If the IPv4 host looks up the IP endpoint by name, the Transformer handles the DNS request,
forwarding it to the network’s DNS when necessary. If the network’s DNS returns an AAAA
record, meaning there is an associated IPv6 address for that name, the Transformer will choose a
surrogate IPv4 address from the address pool and set up a binding for that surrogate IPv4 to the
IPv6 address returned from DNS. The Transformer then passes the surrogate IPv4 address as the
response to the host’s DNS request. If the DNS returns only an A record, that IPv4 address is
transmitted as the answer to the host’s request.
Packets arriving from the network are translated in a complementary fashion. When a packet
arrives at the Transformer for the host’s public IPv4 address, the Transformer replaces that
address with the host’s private address and forwards the packet to the host. When an arriving
packet is addressed to one of the host’s IPv6 public addresses, the Transformer looks up the IPv6