At present, the industry has reached a consensus: IPv6 technology is currently the only feasible solution to address the shortage of IP addresses. However, due to the incompatibility between IPv6 and IPv4 technologies and the existence of a large number of IPv4 devices and users in existing networks, it is necessary to solve the problem of coexistence and interoperability of heterogeneous networks during network evolution.
On February 3, 2011, the Global Internet Assigned Numbers Authority (IANA) officially announced that there was no new IPv4 address allocation. Due to the limited number of IPv4 address resources that China’s operators have applied for, and with the rapid development of applications such as the Internet of Things and mobile Internet, a large amount of address resources will be required, which will inevitably affect the sustained and stable development of China’s Internet. The shortage of IPv4 addresses is imminent.
Essentially speaking, to solve the shortage of IPv4 addresses, two different technical routes can be used. One is a multi-level NAT (such as NAT444) technology, and the other is an IPv6 technology. These two technologies are completely antagonistic. In the long run, NAT technology cannot fundamentally solve the problem of address shortage, and it will increase the complexity of the network structure. At present, the industry has reached a consensus: IPv6 technology is currently the only feasible solution to address the shortage of IP addresses. However, due to the incompatibility between IPv6 and IPv4 technologies and the existence of a large number of IPv4 devices and users in existing networks, it is necessary to solve the problem of coexistence and interoperability of heterogeneous networks during network evolution.
Hotspot transition technology planAt present, the IETF has developed three mechanisms: dual stacks, tunnels, and translation. The dual stack and tunneling mechanism only addresses the coexistence of IPv4 networks and IPv6 networks at the network level. The translation mechanism resolves heterogeneous network services at the service level. Interoperability issues. Since the release of the IPv6 standard, the IETF has developed a variety of different IPv4 and IPv6 coexistence/transition technologies. However, each technology is only applicable to a specific application scenario. When it is actually deployed, it needs to be based on the specific network topology and services. Development needs, using a combination of technologies.
Recently, the IETF v6ops, Behave, and Softwire working groups are working on some new transition technologies such as NAT444, 6rd, DS-Lite, NAT64+DNS64, and IVI. The 6rd and DS-Lite solutions solve the coexistence of heterogeneous networks through tunneling. Problems, to achieve business interoperability also need to combine translation technology; NAT64 + DNS64 and IVI program can solve IPv6 users access to IPv4 network business resources, of which NAT64 is a stateful translation, IVI is a stateless translation.
NAT444The NAT444 uses two-level NAT to implement the mapping of private addresses to private addresses using the first-level NAT in the client network. The second-level NAT is used in the LSN (LargeScaleNAT) of the carrier to implement the mapping from private addresses to public addresses. . The biggest advantage of this solution is that the technology is relatively mature, and a large number of NAT devices have been deployed on the current network, which has a minor impact on the overall architecture of the network. However, the coverage between the client RFC1918 address and the RFC1918 address specified by the operator needs to be considered. , and addressing issues between the same LSN clients. In addition, adopting this solution will delay the transition of the operator's network to IPv6.
6rd6rd is a typical solution for IPv4+6over4 tunnels, and similar solutions include IPv6 overL2TP (providing IPv6 users remote access through L2TP tunnels). 6rd is a scheme for quickly introducing IPv6 based on IPv4 networks. Existing equipments such as broadband access servers in metropolitan area networks do not need to upgrade and support IPv6, 6d gateways are deployed in the metropolitan area network, and IPv6 connections are established between the 6rd gateway and the backbone network. The user's CPE needs to support 6rd. When the user has IPv6 access requirements, an IPv6 over IPv4 tunnel is established between the CPE and the 6rd gateway, IPv6 is forwarded to the 6rd gateway through the tunnel, and the user's IPv4 access continues through the original path. This solution is suitable for the early development of IPv6 services. Operators mainly use IPv4 services and have a small number of IPv6 users.
DS-liteDS-Lite is a typical solution for IPv6+4over6 tunnels. The DS-Lite CGN device is deployed on the metropolitan area network. The broadband access server connects to the core router through IPv6. The user's CPE supports DS-Lite, and the CPE establishes an IPv4 over IPv6 tunnel to the DS-LiteCGN. The broadband access server assigns the user CPE an IPv6 address prefix, and the user host's IPv4 address is assigned by the CPE to an IPv4 private address. The user's IPv6 traffic goes directly to the core router through the broadband access server. After the user's IPv4 traffic reaches the CPE, it passes the IPv4 over IPv6 tunnel to the DS-LiteCGN. The CGN also has the NAT44 function. After the user's IPv4 data is decapsulated through the tunnel, Do another NAT44 address translation and send it to the IPv4 backbone network. One of the benefits of adopting the DS-Lite scheme is to relieve the pressure of the broadband access server equipment, and it can only run the IPv6 protocol stack, which is suitable for use under the IPv6 dominant application scenario.
NAT64+DNS64NAT64+DNS64 is a stateful translation scheme for resolving IPv6 users' access to IPv4 network service resources. In this scheme, the user's applications, access devices, and networks all support IPv6. Users use IPv6 services and content directly, but access to IPv4 services and content will require stateful address translation (NAT64) gateway devices. DNS64 mainly works with NAT64. It mainly synthesizes the A record (IPv4 address) in the DNS query information into the AAAA record (IPv6 address), and returns the synthesized AAAA record user to the IPv6 side user. The user's service traffic will be routed to the NAT64 gateway device based on this destination address. The device translates the destination address and source address and the protocol, and routes to the final server in the form of an IPv4 packet.
IVIIVI is a stateless translation solution for IPv6 users to access IPv4 network service resources. The essence of this solution is to use a part of IPv4 address segments to construct a specific IPv6 address segment, and to form an explicit and specific mapping relationship by embedding IPv4 addresses in IPv6 address segments. There are two major IVI functions: one is address mapping, which is to implement one-to-one mapping between IPv4 addresses and IPv6 addresses through unified rules to translate addresses; the other is protocol translation, which implements the IPv4/ICMPv4 protocol according to the standards. Translates the fields of the IPv6/ICMPv6 protocol and updates the relevant fields of the TCP/UDP protocol to complete the complete packet translation operation.
Carrier network evolution strategyFor operators, IPv6 is the fundamental solution to the problem of IPv4 address shortage. It is also a process of gradual evolution. The following factors must be taken into consideration when selecting transition technologies: the cost of protecting existing networks is reasonable, the difficulty of network transformation is moderate, and existing services are not Impaired, user experience is good. The operator's network can usually be divided into core network, metropolitan area network and access network. Different networks have different evolution routes. For the core network, dual stacks may be used if based on IP technology, and 6PE may be used if based on MPLS technology. For metropolitan area networks, their transition technology solutions should be based on dual-stack technology. Tunnels and translation mechanisms should be combined. Different transition scenarios should be adopted according to different application scenarios. For example, users switch to single-stack IPv6, and 6rd provides IPv6 users' access. In addition, the NAT64/IVI translation mechanism enables IPv6 users to access IPv4 network service resources; content and applications do not change significantly; operators tend to CGN and adopt CGN/NAT444; content and applications do not change significantly; operators tend to use IPv6 and adopt DS-Lite. Provide access for private IPv4 users. Deploy NAT44 to convert private IPv4 to public IPv4. Most content and applications turn to dual stacks and dual stacks. Most content and applications are switched to IPv6, and DS-Lite is used to provide public IPv4 users. The access, NAT64/IVI translation mechanism to achieve IPv4 users access to IPv6 network business resources.
For large Layer 2 access networks, the access device transparently transmits forwarded packets. However, the access device must be able to identify and distinguish between IPv6 packets and IPv4 packets, and perform VLAN tagging, QoS, and packet filtering according to the IPv6 protocol. operating. If dual stacks are supported, IPv6 protocols such as PPPoE and IPoE can be carried directly over data link layer protocols.
Due to the variety of Internet application scenarios, there is no unified mode for the IPv6 evolution technology solution. The evolution of an IPv6 network requires the comprehensive consideration of multiple factors (such as network size, user size, network topology, etc.) to adopt a variety of different technical solutions. The key to the adoption and selection of different IPv6 evolution technologies is often not merely a purely technical reflection. The greater challenge is the impact of Internet development and technology transformation on operations and business models. Therefore, considering different business application scenarios and the future development needs of the network, comprehensive consideration of various factors, combined with a variety of transition technologies to develop strategies for the smooth evolution of the network.
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