Summary of IPv4 to IPv6 transition technology

The two major problems facing internet basic technology IPv4 are address resource depletion and backbone router route table explosion. These two problems are the defects of IPv4 protocol, only a large modification can be done. After years of discussion and comparison and trade-offs of various solutions, the next-generation IP protocol has been basically developed and assigned version 6, called IPv6.

 
One of the key problems facing IPv6's large-scale popularization: How to gradually and without harm transition from an IPv4-based network to an IPv6-based network, while minimizing the cost of transition. IETF has set up a dedicated working group ngtrans to study the transition from IPv4 to IPv6. Currently, three solutions are proposed: Dual stack [5], tunnel [7] and network address/protocol translation (NAPT-PT) [3].

 
As the existing IPv4 network is still working and working well, the cost of upgrading to IPv6 is high, so we can predict, the first upgrade to IPv6 is definitely the special application-driven networks that IPv4 is difficult to meet, such as the Third Generation Mobile Communication (3G) and information appliance. These networks will adopt pure IPv6 instead of IPv4/IPv6 Dual-protocol stacks.

 
However, the vast majority of existing network resources exist in IPv4 networks. It is necessary to ensure that the pure IPv6 network can communicate with the existing IPv4 network. Network Address Translation/protocol translation (NAT-PT) [3] as a technology supporting pure IPv6 network and the existing IPv4 internet transparent communication, has its unique advantages.

 
1 Status of IPv4 to IPv6 transition mechanism

 
In the future, IPv4 and IPv6 will coexist and interact with each other. The evolution from IPv4 to IPv6 is a gradual process. Introducing IPv6 technology and Implementing Global IPv6 network interconnection still takes some time before all services can support IPv6. In this case, it is foreseeable that the transition from IPv4 to IPv6 over the Internet takes a long time to complete and complete the upgrade.

 
Currently, there are three mature technologies to solve the transition from an IPv4 network to an IPv6 network:

 
· Dual Stack Technology );

· Tunnel technology );

· Protocol translation technology (NAT-PT ).

 
1.1 dual-protocol stack technology [5] (Dual Stack, rfc2893)

 
The host runs both IPv4 and IPv6 protocol stacks and supports both Protocols. IPv6 and IPv4 are network-layer protocols with similar functions. Both of them are based on the same physical platform and there is no difference between the transport-layer protocols TCP and UDP attached to them. The protocol stack structure shown in Figure 1 shows that if a host supports both IPv4 and IPv6 protocols, the host can communicate with hosts that support IPv4 protocol, IPv6 can also be used to communicate with hosts that support the IPv6 protocol. This is the working mechanism of the dual-protocol stack technology.

 
Applications

 
Transport Layer Protocol (TCP/UDP)

 
IPv4 protocol IPv6

 
IP layer

 
The title "Double stack" is somewhat misleading. Most IPv6 implementations do not provide two completely different TCP/IP stacks for IPv4 and IPv6 services, but provide a hybrid stack that shares most of the Code in the two protocol stacks.

 
1.2 tunnel technology [7] (Tunnel, rfc3053)

 
This mechanism is used to connect IPv6 sites over an IPv4 network. A site can be either a host or multiple hosts. Tunnel Technology encapsulates IPv6 groups into IPv4 groups. The encapsulated IPv4 groups are transmitted through the IPv4 routing system, and the "protocol" domain of the group header is set to 41, indicates that the load of this group is an IPv6 group, so that the encapsulated IPv6 group can be restored and transmitted to the target site in a proper place. Tunnel Technology only needs to be modified at the entrance and exit of the tunnel, and has no requirements on other parts, so it is very easy to implement. However, tunnel technology cannot directly communicate with IPv4 hosts and IPv6 hosts.

 
1.3 NAT-PT [3] technology (Network Address Translation-protocol translation, rfc2766)

 
Rfc1631 describes in detail the basic principles of the NAT (network address translator) technology. Although NAT technology is designed for IPv4 networks, as long as IPv4 addresses and IPv6 addresses are regarded as internal addresses and global addresses in NAT technology respectively, it can be applied to the evolution of IPv6 technology, in this case, Nat becomes Nat-Pt. Using the translation gateway to convert IP header addresses between IPv4 and IPv6 networks, and performing semantic translation on the groups based on different protocols, the pure IPv4 and pure IPv6 sites can communicate transparently.