Cisco Cisco IOS Software Release 12.2(1c) White Paper
![Cisco](https://files.manualsbrain.com/attachments/7380d0050044647c30f5c24bbbf5d0c0b6d9bb84/common/fit/150/50/faa183d287233c52228cfea3dbc2a127fe780f60564fcb0955d9c3d1cd23/brand_logo.png)
White Paper
All contents are Copyright © 1992–2007 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
Page 2 of 19
Deployment Areas
NAT-PT will likely be deployed in these networking environments:
●
Enterprises: Enterprise customers may maintain IPv4-only hosts for several years before
upgrading to IPv6 (e.g. IPv4-only Token-Ring PC communicating with IPv6-only PDA
devices), depending on their applications. At the same time, it is expected that IPv6-only
hosts will be configured, even on capable of Dual Stack Operating System, to get benefit of
the IPv6 auto-configuration, global addressing and simpler management (no dual-protocol).
●
ISPs: ISP offering IPv4 and IPv6 connectivity and services will look at providing
communications between both protocol versions, i.e.: an IPv6-only client accessing an
IPv4-only web server. NAT-PT is an added-value capability in an ISP POP site. In an IPv4-
only legacy server farm, the addition of NAT-PT routers would open it to the new IPv6 world
at a low cost.
●
Homes: New IPv6-only Internet appliances (i.e.: mobile phones, PDAs, refrigerators, and
audio components) will become available in the future. Home users will not focus on the IP
version supported by these classes of product. ISPs can seize this opportunity by offering a
NAT-PT service, and thus decreasing the complexity for home users.
NAT-PT Architecture
With NAT-PT, sessions can be initiated from IPv4 and IPv6 hosts, because bi-directional
connections are established. IPv6 addresses are mapped to IPv4 addresses and vice and versa,
statically or dynamically. The source IP address and related fields (i.e.: IP headers and ICMP
headers) are translated for those packets leave one realm for another.
In the vast majority of the cases, DNS is used for IPv4 to IPv6 and IPv6 to IPv4 communications,
as it is the common way to access an IP host. As a result, DNS requests cross the NAT-PT box. A
DNS-ALG must be implemented in NAT-PT routers to facilitate name to address mapping. The
DNS-ALG is capable of translating IPv6 addresses in DNS queries and responses into their IPv4
address bindings (and vice versa), as DNS packets traverse between IPv6 and IPv4 realms.
NAT-PT Operations
This section details all the steps of a data communication crossing a NAT-PT router in the
following environment (Figure 1).
Figure 1. A Basic NAT-PT Topology
NAT-PT Communications with Static Mapping
IPv6 Initiated Communications
In the case of an IPv6 initiated communication between Hosts A and B, the data communication
follows the sequence depicted in Figure 2. Storing static IPv6 to IPv4 address correspondences in
the NAT-PT router configuration creates static mapping.