NAT, IPv4 to IPv6

- IPv6 Migration Technologies

 The key to success in the IPv6 migration process resides in such compatibility: in being able to use both IPv4 and IPv6 protocols until all the services migrate to IPv6. 

Most Internet’s nodes are going to need to use both protocols (IPv4 and IPv6) for a long time. Because of this, it is very important to analyze the migration methods to IPv6 and to chose the most suitable one, depending on the operator’s network. 

It is known that any attempt to have a quick transaction is destined to fail and that gradual transaction schemes are needed. 

- Network Address Translation (NAT)

Network Address Translation (NAT) is the process of mapping multiple private IP addresses to a single public IP address. This is done by network devices (such as routers or NAT firewalls) when transmitting information.

NAT is used by organizations that have multiple devices and need to access the Internet from a single public IP address. Most home routers will also work with it.

NAT improves security and reduces the number of IP addresses an organization requires. However, it can also cause path delays and prevent some applications from accessing the private network model.

- NAT Techniques

Network address translation (NAT) is a technique that translates IPv4 addresses into IPv6 addresses and vice versa. NAT allows IPv6-only devices to communicate with IPv4-only devices, and vice versa. 

NAT techniques include: 

• NAT64: A gateway that translates between IPv4 and IPv6 protocols
• NAT46: Works with DNS64 to translate between IPv4 and IPv6 protocol stacks

NAT works by changing the headers of IP packets as they travel through a router. For example, when a client accesses the Internet using IP 10.0.0.1, source port 8000, NAT will change the source IP to 202.123.211.25, but the port number remains the same. This is called port protection.

Some disadvantages of NAT include:

• Path delay
• Block certain applications from accessing the private network model
• Router tampering with port number

NAT was created to address IP starvation. However, IPv6 solves this issue, so NAT is no longer needed. IPv6 is faster than IPv4 in network devices because it lacks NAT.

- IPv6 NAT

IPv6 NAT is a network address translation (NAT) mechanism that translates IPv4 addresses to IPv6 addresses. IPv6 NAT also translates addresses between IPv6 hosts. 

IPv6 NAT supports three types of NAT: 

• Source NAT: Translates the source IP address of a packet leaving a network device. Source NAT allows a host with a private IP address to access the public network.
• Destination NAT: Translates addresses between IPv6 hosts.
• Static NAT: Translates IPv4 addresses to IPv6 addresses of network devices.

IPv6 removes most of the need for NAT. However, there are rare situations that call for the use of NAT with IPv6, such as: 

• Multi-WAN for IPv6 on residential or small business networks
• NAT64, which facilitates communication between IPv6 and IPv4 hosts
• NPTv6, which performs stateless translation of one IPv6 prefix to another IPv6 prefix

NAT exists to overcome a shortage of IPv4 addresses. Because IPv6 has no such shortage, IPv6 networks do not require NAT.

(Available IPv6 Transition Technologies - Cisco)

- NAT-PT

NAT-PT stands for Network Address Translation and Protocol Translation. It allows IPv4 and IPv6 nodes to communicate by translating between IPv4 and IPv6 packets. NAT-PT can be done in two directions, from IPv6 to IPv4 and vice versa. 

• NAT-PT performs the following: 
• Translates an IPv4 address into an IPv6 address and vice-versa
• Translates an IPv4 packet into a semantically equivalent IPv6 packet and vice-versa
• Maps the destination host to a local address
• Translates the source ad 
• Sends a ICMP/ICMPv6 Message Too Big packet back to the sender if a packet is too large to be transmitted on the outbound network

NAT-PT is defined in RFC 2765 and RFC 2766. A proper NAT-PT implementation requires a number of specific ALG (application level gateways) to be used along with NAT. The purpose of ALGs is to resolve application-level issues that arise from the IP address change. 

For example, NAT-PT can enable a host in an IPv6 network to access the FTP server in an IPv4 network.

- Cisco NAT64 Technology

Connecting IPv6 and IPv4 Networks - three main options are available for migration to IPv6 from the existing network infrastructure: dual-stack network, tunneling, and translation.   

• Dual-Stack Network: Dual stack is a transition technology in which IPv4 and IPv6 operate in tandem over shared or dedicated links. In a dual-stack network, both IPv4 and IPv6 are fully deployed across the infrastructure, so that configuration and routing protocols handle both IPv4 and IPv6 addressing and adjacencies.
• Tunneling: Using the tunneling option, organizations build an overlay network that tunnels one protocol over the other by encapsulating IPv6 packets within IPv4 packets and IPv4 packets within IPv6 packets. The advantage of this approach is that the new protocol can work without disturbing the old protocol, thus providing connectivity between users of the new protocol.
• Translation: Address Family Translation (AFT), or simply translation, facilitates communication between IPv6-only and IPv4-only hosts and networks (whether in a transit, an access, or an edge network) by performing IP header and address translation between the two address families.

Please refer to Cisco NAT64 Technology: Connecting IPv6 and IPv4 Networks for more details.

However, it seems like the industry is taking a long time to migrate from IPv4 to IPv6. Part of the reason is that network address translation (NAT) helped delay the transition. NAT makes it possible to direct traffic to thousands and thousands of individual IP addresses on private networks through NAT gateways that each use up just one public IP address.  

[More to come ...]