Datatek IPv6 Transformer User Manual - Manual (Page 16)

S E C T I O N 2 O V E R V I E W
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The Transformer has a feature called Local Forwarding, which is used to add extra IPv4 host
nodes with IPv4-IPv6 packet translation. This functionality is directed by ‘forward mapping’.
Without any forward mappings, the Transformer acts as a full IPv6 surrogate for one IPv4 host.
With forward mapping enabled, the Transformer can perform address and protocol translation
for additional IPv4 endpoints on the host-side network. However, the Transformer cannot act as
a full IPv6 surrogate for those other IPv4 endpoints.
The mappings added for forwarding are different from the primary address bindings. The
primary bindings (static, DNS and ingress) map existing IPv6 addresses into surrogate IPv4
addresses, seen only on the host-side network, that allow host-side endpoints to reach the IPv6
world using IPv4 addresses. Bindings for forwarding map existing IPv4 addresses on the host
side into surrogate IPv6 addresses that network-side endpoints can use to reach endpoints on the
host side through the Transformer.
The extra surrogate IPv6 addresses allow the Transformer to perform packet translation between
IPv4 endpoints on the host side (other than the host itself) and IPv6 endpoints on the network
side. However, they do not provide full Transformer functionality for those endpoints. For
example:
- The DHCP6 client cannot obtain IPv6 addresses for these endpoints
- The Transformer cannot auto-configure any IPv6 addresses, e.g. link local for these
endpoints
- There is only one IPv6 address assigned to each IPv4 address, and therefore only one IPv6
scope for any endpoint set up this way
- IPv4 passthrough cannot be done to these extra hosts
Using forward mapping and static routes, the IPv4 address space on the host side can be more
elaborate than just a simple host subnetwork. For example:
- The host or some other endpoint on the host side can provide forwarding; the Transformer
can be configured with an appropriate static route. This may allow IPv4 passthrough
- The surrogate IPv6 addresses used in forward mapping can belong to an IPv6 subnetwork
different from the Transformer; a router on the IPv6 network side can be configured to
forward those addresses through the Transformer.
Complications can easily cause serious problems. For example:
- A DHCP server on the host side can interfere with the Transformer
- Any endpoint on the host subnetwork that is not in the local forwarding list will have an arp
conflict with the Transformer
- IPv4 connectivity of any equipment on the host side that might reach the main network (on
the Transformer’s IPv6 side) without going through the Transformer might cause problems
Figure 4. Local Forwarding,
shows a primary IPv4 device and other secondary IPv4 endpoints
behind the Transformer.