Next Generation Internet 4over6 soft line Tunnel Transition Technology

After more than 20 years of rapid development, the Internet based on IPv4 protocol has achieved great success in the world. However, with the continuous growth of the Internet scale, new demands, and new business development, the IPv4-based network environment is hard to cope with. The rapid expansion of the network scale highlights a series of serious problems of IPv4, these include insufficient address resources, insufficient routing scalability, and end-to-end feature damage caused by Network Address Translation (NAT) technology.

IPv6 is a basic network protocol that replaces IPv4 in the Next Generation Internet. Because IPv6 is not compatible with IPv4, the Internet is faced with heterogeneous routing, scalability, status maintenance, and other issues during the transition from IPv4 to IPv6. In addition, because most network resources, services, and applications are still implemented based on IPv4, end users are still dependent on IPv4, and Internet service providers (ISPs) have some inertia for IPv6 upgrade, as well as insufficient IPv6 support for network devices, especially access network devices, it is foreseeable that IPv4 and IPv6 will coexist for a long period of time. During the coexistence of the two, how to quickly transition the entire network to IPv6, especially the access network, has become the key to restricting the development of the next generation Internet.

Many transition technical solutions have been proposed for IPv6 transition. These solutions are classified by technical ideology and can be divided into tunneling and translation technologies. Based on the concept of tunnel transition, this paper proposes an IPv6 tunnel transition framework system for the entire network, as well as the 4over6 soft-line tunnel technology applicable to the transition between the backbone network and the access network. At present, the 4over6 soft-line Tunnel transition scheme and related technologies have formed three international standards in the IETF of the international Internet Standardization Organization, including RFC4925, RFC5565, and rf120047, the China Communications Standardization Association has formed two standards for the China communications industry.

1. network-wide IPv6 tunnel Transition Framework and Policy

The IPv6 transition technology solution for the entire network must meet the following requirements:

(1) maintain the end-to-end feature, which is a basic requirement for achieving two-way communication between the terminal node and the Internet.

(2) Maintaining the scalability of heterogeneous networks, that is, the independence and scalability of IPv4 and IPv6 routes, this is an important guarantee for smooth IPv6 transition when the existing IPv4 network is minimized during the transition period.

(3) transparent presentation of upper-layer mobile applications, which is the key to maintaining existing IPv4 applications during the IPv6 transition period and ensuring a good network experience for users.

The network-wide IPv6 tunnel transition problem can be divided into backbone network IPv6 transition and access network IPv6 transition according to different network levels, as shown in tunnel transition framework 1. The backbone network connects to the ISP network up, other backbone networks at the same level, and the access network down. The access network connects to the backbone network to provide access to different types of users. There are several border routers (BRS) connected to the edge routers (PES) on the adjacent side of the access network and the backbone network. The transition of the backbone network tunnel requires that the PE be upgraded to the dual-stack mode. The PE uses tunnels to provide transparent transmission for groups with different backbone network address clusters. Tunnel transition requires both the BR and the user-side edge device (CE) to maintain the dual stack. CE creates a tunnel for the group of different address clusters of the access network and sends it to the BR, in this way, the CE and BR use tunnels to provide transparent transmission for groups with heterogeneous access network address clusters.

Figure 1 network-wide IPv6 tunnel Transition Framework

The network-wide tunnel transition route is a process from IPv4 to IPv6 over IPv4 to dual-stack to IPv4 overIPv6 to IPv6. In the early stage of transition, some IPv6 Access Network islands emerged. These networks need mutual access and access to the IPv6 internet. At this time, because IPv4 transmission is still the mainstream, a large number of backbone network core routers (P) are still IPv4 single-stack, it is difficult to upgrade these routers to dual-stack.

Therefore, a few PE routers should be upgraded to dual-stack routers, and IPv6 islands should be provided with IPv4 transmission services through the 6over4 tunnel. The P router of the backbone network will start the IPv6 protocol stack on the basis of running IPv4, that is, upgrade to dual-stack. As the scale of the double-stack P router increases, the corresponding O & M overhead also increases, while IPv4 transmission requires less and less. Therefore, the P router will gradually close the IPv4 protocol stack and only run the IPv6 Single stack; the PE router maintains the dual-stack mode and provides IPv4 networks with cross-transmission services through the 4over6 tunnel. In the end, IPv6 is fully deployed in the whole network, and the network fully implements the transition to IPv6.

2 IPv6 backbone network 4over6 soft line Tunnel Technical Principle and Application

The External Border Gateway Protocol (EBGP) is run between the PE at the edge of the backbone network and the upper-level, the access network, and the same-level backbone network to transmit Inter-Domain Routing information, while the backbone router (PR) on the inside of the backbone network) through the internal Border Gateway Protocol (IBGP. The main task of the backbone network is to provide IPv4 and IPv6 Access and transmission services. In the IPv6 single-stack backbone network, you need to deploy and implement the backbone network 4over6 soft-line tunneling technology.

The 4over6 soft line tunnel technology uses an automatic tunnel mechanism to establish a 4over6 soft line tunnel.

The 4over6 soft-line tunneling technology expands the Core routing protocol of IPv6 backbone network-multi-protocol Border Gateway Protocol (MP-BGP) by 4over6.

This extension enables MP-BGP packets to carry IPv4 destination network information and tunnel endpoint information and send it to the other end of IPv6 backbone network, the hybrid transmission of IPv4/IPv6 routes allows you to build stateless 4over6 soft-line Tunnels between PES. You can use the IPv4 routing protocol between the PE and the CE to exchange IPv4 routing, or you can configure the default route from the CE to the PE. PE needs to encapsulate, unencapsulate, and forward the group.

After the entry PE finds the proper exit PE through IPv4 routing, the entry PE needs to encapsulate and forward the original IPv4 group by using the IPv4-in-IPv6 sealing mechanism. After receiving the IPv4-in-IPv6 encapsulation group on the IPv6 backbone network, the egress PE unencapsulates the group and forwards it to the corresponding IPv4 destination network.

At present, backbone network 4over6 soft-line tunneling technology has formed two international standards RFC5565 and rf000047 in IETF, and has been deployed in the world's largest IPv6 single-stack backbone network-CNGI-CERNET2, formed a 4over6 soft-line Tunnel transitional trial commercial system with hundreds of colleges and universities participating in the campus network. Backbone Network 4over6 soft line tunneling technology is shown in CNGI-CERNET2 deployment 2. The backbone network 4over6 soft-line tunnel technology is deployed in combination with the actual network operation conditions of major universities, which can be well isolated from the existing routes on the campus network, without affecting the existing campus network, at the same time, it can well meet the deployment needs. The deployment and test results show that the 4over6 soft-line tunnel technology of the backbone network has small changes to the backbone network, simple equipment configuration, high scalability, and low maintenance burden, protecting the investment of original network equipment, it can support various typical IPv4 applications such as WEB and P2P, and has good operational performance.

Figure 2 Introduction of backbone network 4over6 soft wire tunneling technology in CNGI-CERNET2

3 IPv6 Access Network 4over6 soft-line Tunnel Technical Principle

The main task of the access network is to provide services for the access to the backbone network or the internet for the user's edge devices. To achieve this goal, the IPv6 single-stack backbone network needs to be deployed to implement the 4over6 soft-line tunnel technology of the access network.

The architecture of the 4over6 soft-line tunnel for the access network is shown in 3. The CE, as the starting point of the 4over6 tunnel, can be either a terminal host or a user station equipment (CPE), such as a home gateway, collectively referred to as 4over6 CE. The 4over6 BR is maintained by the ISP as the convergence point of the 4over6 soft-line tunnel. It is deployed at the junction of the ISP IPv6 network (IPv6 Access Network) and IPv4 internet (or Backbone Network, all IPv4 packets sent to and from the ISP network must pass through 4over6 BR.

Figure 3 architecture of access network 4over6 soft-line Tunnel

On the control layer, the 4over6 ce in the IPv6 network accesses the IPv4 internet through an adaptive heterogeneous dynamic access mechanism.

The DHCP server assigned an IPv4 address for 4over6 CE is maintained by the ISP. It can be jointly deployed with 4over6 BR or deployed as an independent DHCPv4 server and 4over6 BR In the same IPv4 network. Because 4over6 CE and 4over6 BR are connected through a pure IPv6 Access Network, the traditional Dynamic Host Configuration Protocol (DHCP) cannot run normally in the IPv6 network, therefore, the 4over6 soft-line tunnel technology of the access network expands the traditional DHCP, and uses the DHCPv4 over IPv6 Extension Mechanism Based on IPv6 transmission for IPv4 address allocation. The DHCPv4 over IPv6 mechanism has two scenarios, as shown in figure 4. Figure 4 (a) shows that the DHCPv4 client communicates with the IPv6 extended DHCP server (TSV) through the customer relay proxy (CRA), while Figure 4 (B) as shown in, the DHCPv4 client communicates with traditional DHCP servers through the CRA and IPv6 transmission relay proxy (TRA.

Figure 4 application scenarios of the DHCPv4 over IPv6 Mechanism

The CRA and DHCPv4 clients are in the same host and are responsible for relay the DHCPv4 information between the DHCPv4 client and TSV/TRA. CRA communicates with the DHCPv4 client through IPv4 and TSV/TRA through UDPv6 packets. TRA is deployed between an IPv6 network and an IPv4 network. It is responsible for relay DHCPv4 messages between CRA and traditional IPv4 DHCPv4 servers. TSV is a DHCP server that supports IPv6 packet transmission. It is deployed in an IPv6 network and transmits DHCP data carried by IPv6 packets with CRA or TRA to complete interaction with the DHCP Client and assign an IPv4 address to the client host. Through this mechanism, the DHCP client can obtain the IPv4 address and other resources allocated by TSV without any changes.

On the data layer, the encapsulation and encapsulation of the IPv4-in-IPv6 are completed at both ends of the 4over6 soft line tunnel, 4over6 CE and 4over6 BR respectively.

When 4over6 CE needs to initiate communication to 4over6 BR, 4over6 CE first encapsulates IPv4 packets based on the IPv6 address of the Local Machine and the IPv6 address of the 4over6 BR, the original IPv4 packet is used as the load of IPv6 packets. Then, the 4over6 CE sends the packet to the IPv6 network, and the packet is sent to the 4over6 BR through the IPv6 network. After receiving the packet, 4over6BR first unpacks the IPv6 packet and restores it to an IPv4 packet. Then 4over6 BR submits the packet to the IPv4 network for subsequent forwarding.

When the 4over6 BR needs to initiate a communication to the 4over6 CE, The 4over6 BR first checks the 4over6 CE-side IPv6 address and IPv4 address ing table maintained on the local machine and matches the IPv4 packet Destination Address and ing record, find the corresponding IPv6 address as the destination address of the IPv6 Header, and use the IPv6 address of the 4over6 BR local machine as the source address to encapsulate the IPv4 packet header, the IPv4 header and the content inside it become the load of IPv6 packets. Then the 4over6 BR sends the packet to the IPv6 network, and the packet is sent to 4over6 CE through the IPv6 network. After receiving the message, 4over6 CE unpacks Its IPv6 packet header, restores the packet to an IPv4 packet, and forwards it to the upper-layer application.

4over6 BR records 4over6 CE IPv4-IPv6 address correspondence information through lightweight user-level State maintenance. 4over6 BR does not care about the number of sessions established by 4over6 CE. It only maintains the ing between the IPv6 address and IPv4 address of 4over6 CE. Therefore, this is a ing between the status of each user and the stateless status of each stream. The user-level status maintenance mechanism greatly reduces the O & M overhead of 4over6BR, reduces the ISP network burden, and improves the network experience of end users.

4 IPv6 Access Network 4over6 soft-line tunnel technology system development and deployment test

Tsinghua University has completed the implementation of a 4over6 soft-line Tunnel software system based on Linux, Windows 7 and Android systems. The source code of the software system was open-source on Github in 2012. The open-source project will make an important contribution to expand the impact of technical solutions and attract peers to participate in technical solutions.

At present, the network access 4over6 soft-line Tunnel transition scheme and related technologies have already formed a number of draft standards in the IETF softwire and dhc working groups, which has aroused widespread attention in the industry. In promoting the standardization of technical solutions, Tsinghua University has also led a number of Chinese equipment manufacturers to implement the 4over6 soft line tunnel technology. The prototype system of the 4over6 soft-line tunnel technology is formed based on the technologies of various software and hardware platforms. On this basis, Tsinghua University conducted a technical test and deployment of the 4over6 soft-line tunnel over the IPv6 campus network, as shown in Figure 5. In addition, China Telecom deployed an IPv4 and IPv6 Dual-stack environment for the broadband network in Hunan province, and completed the test deployment of the lightweight 4over6 soft line tunnel technology LAFT6. The experiment and test deployment results show that the 4over6 soft-line tunnel technology of the access network is simple, easy to deploy, with low O & M overhead and high scalability, and can provide good support for existing IPv4 applications and services.

Figure 5 experimental deployment of IPv6 campus network at Tsinghua University

5 conclusion

Aiming at the key technical problems of next-generation Internet IPv6 transition, this paper studies the transition from the perspective of tunnel, and proposes the technical solution of 4over6 soft-line tunnel for the full-network IPv6 transition. In response to the IPv6 transition requirements of the entire network, the technical solution puts forward the 4over6 soft-line tunnel technology applicable to the backbone network and the access network respectively, forming a unified technical system for tunnel transition, the entire IPv6 network can be smoothly transitioned through mechanisms such as isolation of heterogeneous routes in the backbone network, adaptive heterogeneous dynamic access to the access network, and transparent automatic tunnel. At present, the 4over6 soft-line Tunnel technical solution has formed three IETF international standards and two national communication industry standards. Based on the research and standardization of technical solutions, the 4over6 soft line tunnel technology has completed the development, application and deployment of a number of systems. The applications, experiments, and deployment results show that the 4over6 soft line tunnel technology has the advantages of simplicity, ease of configuration and deployment, low O & M overhead, and good support for IPv4 applications and services, it provides an important solution to promote the Next Generation Internet IPv6 transition.