CN110691150A

CN110691150A - SDN-based IPv4 and IPv6 interconnection method and system

Info

Publication number: CN110691150A
Application number: CN201910934293.3A
Authority: CN
Inventors: 陆以勤; 李智鹏; 覃健诚; 程喆
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2019-09-29
Filing date: 2019-09-29
Publication date: 2020-01-14

Abstract

The invention discloses an IPv4 and IPv6 interconnection method and system based on SDN, wherein the method comprises the following steps: when an IPv6/IPv4 client initiates access to an IPv4/IPv6 network by using a domain name of the IPv4/IPv6 network, the request is inquired and transferred through an SDN, the request data and the request for converting control records are inquired, the IPv4/IPv6 receives the converted request for recording inquiry and inquires the domain name in the network, then replies a recording inquiry response carrying an IPv4/IPv6 address, after the domain name is inquired and transferred again through the SDN, translated and replied, the IPv6/IPv4 client sends a first data packet by using the received translated address as a destination address, sends the data packet to the IPv4/IPv6 network after the SDN is transferred and translated, receives a reply data packet of the IPv4/IPv6 network, then translates the data packet into a fourth data packet and sends the fourth data packet to the IPv6/IPv4 client, and the IPv6/IPv4 client receives the fourth data packet. The invention can realize that only one routing table item of the SDN controller of the SDN network is added on the basis of the traditional network, and the interconnection between the IPv4 and the IPv6 is completed.

Description

SDN-based IPv4 and IPv6 interconnection method and system

Technical Field

The invention relates to the field of network communication, in particular to an IPv4 and IPv6 interconnection method and system based on SDN.

Background

With the expansion of network size and the generation of various new applications, the IPv4 network is exposed to more and more problems, and the cost for completely upgrading the current IPv4 network into the IPv6 network is enormous, so that the IPv4 and the IPv6 will exist simultaneously in a long time in the future. In order to ensure the continuity of network traffic, an IPv6 transition technology must be introduced in the stage of coexistence of IPv4 and IPv6. Each of the transition techniques currently used is only specific to a particular application requirement and is not universal. Therefore, in actual deployment, devices with corresponding functions are added to the network according to specific application requirements, which not only increases the complexity of network functions, but also causes resource waste due to complex configuration.

Upgrading the current IPv4 network entirely to an IPv6 network requires not only support from the device, but also rewriting the current network application entirely with the IPv6 protocol, at a cost that is difficult to estimate. Therefore, upgrading from IPv4 to IPv6 is not completed in a short time, but is a growing and lengthy process in which IPv4 and IPv6 coexist. In the process of upgrading IPv4 to IPv6, the original network service cannot be interrupted, so that an IPv6 transition technology must be introduced in the stage of coexistence of IPv4 and IPv6, on one hand, the multiplexing of IPv4 addresses is realized in the stage of coexistence of IPv4 and IPv6, and the consumption of IPv4 public network addresses is reduced; on the other hand, the interconnection and the intercommunication between the IPv4 and the IPv6 are realized through translation conversion between the IPv4 and the IPv6, so that the continuity of the current network service is ensured. At present, a plurality of transition technologies have been developed to meet different requirements, including a dual stack technology, a tunneling technology, a translation technology, etc., each transition technology is only specific to a specific application requirement and has no universality, so that in actual deployment, a device with a corresponding function needs to be added to a network according to the specific application requirement, which undoubtedly increases the complexity of the network. In addition, due to the change of the network application requirements, the deployment of the network needs to be changed according to the change of the requirements, which not only increases the complexity of the network deployment configuration but also causes waste of network resources. With the advent of a new network architecture called Software Defined Networking (SDN), these difficulties encountered in traditional IPv6 transition technologies may find a new solution.

The SDN is a novel network architecture provided by Clean Slat research group of Stanford university, and the original point is that network control and network forwarding decoupling in the traditional network are separated into a control plane and a data plane, the control plane opens a standard control interface to the outside, and a network administrator can use the control interfaces to write specific network application programs so as to achieve control on specific requirements of the network. And the data plane only carries out processing such as forwarding and the like on data communication in the network according to commands from the control plane. In the SDN network, an SDN controller serving as a control plane senses the entire network, maintains the topology of the entire network, makes a network policy, issues a policy, and the like, and an SDN switch serving as a data plane completes packet forwarding and the like according to the policy issued by the controller. Once the SDN is released, IT is widely focused by academic circles and business circles in an open, flexible and fine-grained network management control manner, and both world-known network equipment providers and network operators such as cisco, huayao, AT & T, and the like and well-known IT industry capitals such as microsoft, google, IBM, and the like show a high attention to the SDN, so that the SDN is likely to become a direction of a next-generation internet architecture.

After the emergence of the SDN, attention and applications have been paid to many aspects, such as network security, QoS guarantee, flow control, etc., but how to introduce a combination SDN technology in the conventional IPv6 transition technology to solve the complexity of the network and the sustainability of services in the stage of coexistence of IPv4 and IPv6 has not been intensively studied at present. The research of the interconnection technology of IPv4 and IPv6 made on the basis of the SDN framework has certain theoretical and practical significance.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide an IPv4 and IPv6 interconnection method and system based on an SDN (software defined network), which can realize that only one routing table entry of an SDN controller of the SDN is added on the basis of the traditional network to complete the interconnection of IPv4 and IPv6.

The purpose of the invention is realized by the following technical scheme: an SDN-based IPv4 and IPv6 interconnection method comprises the following steps:

when an IPv6/IPv4 client accesses an IPv4/IPv6 network by using the domain name of an IPv4/IPv6 server, a domain name first record query request is initiated to an SDN controller, and the resource type of the first record query request is matched with the resource type of DNS6/DNS 4;

calling a domain name resolution management module through an SDN controller, if the domain name resolution management module cannot query the corresponding resource record, converting the first record query request into a second record query request, wherein the type of the second record query request is matched with the DNS4/DNS6 resource type, and sending the second record query request to a domain name server DNS4/DNS6 in an IPv4/IPv6 network;

when the DNS4/DNS6 receives the second record query request, the queried domain name is found to be the domain name in the network of the DNS, a second record query response carrying an IPv4/IPv6 address is generated through the DNS4/DNS6, and the second record query response is replied to the SDN controller;

translating the received second record query response into a corresponding first record query response through an SDN controller, translating the carried IPv4/IPv6 address into a corresponding IPv6/IPv4 address, and returning the corresponding IPv6/IPv4 address to the DNS6/DNS 4;

after receiving the reply of the SDN controller, the DNS6/DNS4 replies the received query response to the IPv6/IPv4 client;

sending a first data packet in an IPv6/IPv4 format to the SDN by the IPv6/IPv4 client by taking the received IPv6/IPv4 address as a destination address (the first data packet reaches the SDN through a boundary router);

calling a network layer protocol conversion module through the SDN, translating the first data packet in the IPv6/IPv4 format into the first data packet in the IPv4/IPv6 format, and sending the first data packet to the IPv4/IPv6 network;

after the IPv4/IPv6 network receives the first data packet, replying the second data packet in the IPv4/IPv6 format to the IPv6/IPv4 client;

calling a network layer protocol conversion module through the SDN, translating the second data packet in the IPv4/IPv6 format into an IPv6/IPv4 second data packet, and sending the second data packet to the IPv6/IPv4 network;

the IPv6/IPv4 client receives the second data packet.

Preferably, the translation behavior complies with the IP/ICMP translation algorithm defined in RFC6145 standard; specifically, the IPv4 address is translated into the IPv6 address according to the algorithm defined in RFC 6052; the SDN calls a network layer protocol conversion module, and the IPv6/IPv4 format data packets are translated into IPv4/IPv6 format data packets, so that the general NAPT mapping rule RFC3022 is met.

Preferably, the step of translating the IPv6 address into the corresponding IPv4 address is:

sending an address application request to an address management and mapping module through a domain name resolution management module;

selecting an available IPv4 address from the address pool through the address management and mapping module, returning the address to the domain name resolution management module, and establishing an address binding relationship;

and synthesizing the received second record query response into a corresponding first query response according to the returned address by the domain name resolution management module, and returning the corresponding first query response to the DNS 4.

Preferably, the network layer protocol conversion module is called by the SDN to translate the IPv6 format data packet into an IPv4 format data packet, and the specific steps sent to the IPv4 network are as follows:

the SDN controller calls an address management and mapping module to inquire whether a source IPv6 address has a mapping relation in an address translation table or not after receiving a communication data packet from an IPv6 client to an IPv4 server through the SDN switch and finding that the destination address is an IPv4 mapping address;

if not, selecting an idle address from the IPv4 address pool to the source IPv6 address, converting the idle address into an IPv4 address serving as a new source address, establishing a mapping relation, and converting the destination address into an IPv4 address according to a corresponding rule;

and translating the IPv6 format data packet into an IPv4 format data packet by a network layer protocol conversion module, and sending the IPv4 format data packet to the IPv4 server.

Preferably, the network layer protocol conversion module is called by the SDN to translate the IPv4 format data packet into an IPv6 format data packet, and the specific steps sent to the IPv6 network are as follows:

receiving a communication IPv4 format data packet from an IPv4 client to an IPv6 server through an SDN switch, finding that a destination address is an IPv6 mapping address, calling an address management and mapping module by the SDN controller, and inquiring whether a source IPv4 address has a mapping relation in an address translation table;

if not, selecting a free address from the IPv6 address pool to the source IPv4 address, converting the free address into an IPv6 address by the network layer protocol conversion module to serve as a new source address, establishing a mapping relation in an address conversion table, and converting the destination address into an IPv6 address according to a corresponding rule;

and translating the IPv4 format data packet into an IPv6 format data packet by a network layer protocol conversion module, and sending the IPv6 format data packet to the IPv6 server.

An SDN-based IPv4 and IPv6 interconnection system comprises an SDN controller, an SDN switch, a routing module and an interconnection module;

the routing module is installed in the SDN controller and used for network routing of communication data packets between networks; the system specifically comprises a route configuration submodule, a route detection submodule and a route management submodule;

the routing configuration submodule is used for configuring the border routing gateway equipment;

the route detection submodule is used for detecting the border route gateway equipment;

the routing management submodule is used for maintaining and managing information such as a routing table and the like;

the interconnection module is used for acquiring IP addresses, managing, mapping and converting IPv4 addresses and IPv6 addresses and translating protocols of IPv4 format data packets and IPv6 format data packets; the interconnection module specifically comprises a domain name resolution management submodule, a network layer protocol conversion submodule and an address management and mapping submodule;

the domain name resolution management submodule is arranged in the SDN controller and used for agent query and result conversion and helping a client to obtain an address embedded with a destination address;

the network layer protocol conversion submodule is installed in an SDN switch and is used for protocol translation and address conversion between an IPv4 data packet and an IPv6 data packet in the data communication process;

the address management and mapping submodule is installed in the SDN controller and used for dynamically managing the IPv4 address and the IPv6 address in the DNS analysis stage and establishing the mapping relation between the IPv4 address and the IPv6 address.

Preferably, the routing module, the domain name resolution management submodule and the address management and mapping submodule are installed and added into the SDN controller in a plug-in mode.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. according to the invention, only one routing table entry of the SDN controller of the SDN network is added on the DNS server, namely, the mapping relation between the IPv4 address and the IPv6 address is established through the address management and mapping sub-module installed on the SDN controller, and the invention has less change on the traditional network.

2. The client of the IPv4 or IPv6 network in the invention does not need to care about whether the address corresponding to the domain name is IPv4 or IPv6, and can access the service only by inputting the domain name, so the invention has strong transparency.

3. The invention uses the control plane to write the application program for realizing the interconnection function of the IPv4 and the IPv6 to the standard control interface provided on the SDN controller and the switch, and then the application program is installed and added into the SDN controller and the switch in the form of plug-in, and the invention does not need some network application functions in the future and only needs to remove the related application modules from the controller and the switch. Therefore, the invention is flexible and convenient.

4. The network layer protocol conversion sub-module is installed and added into the SDN switch in the form of plug-in, so that the congestion of an SDN controller can be effectively avoided.

Drawings

Fig. 1 is a schematic diagram of an SDN-based IPv4 and IPv6 interconnection system model according to embodiment 3 of the present invention;

FIG. 2 is a schematic diagram of the process communication between an IPv6 client and an IPv4 server;

fig. 3 is a flowchart of an IPv6 client accessing an IPv4 server according to embodiment 1 of the present invention;

fig. 4 is a flowchart of an IPv4 client accessing an IPv6 server according to embodiment 2 of the present invention.

Detailed Description

For better understanding of the technical solutions of the present invention, the following detailed description is provided for the embodiments of the present invention with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

As shown in fig. 3, this embodiment discloses a communication method in which a client in an IPv6 network is used as an initiating host to access a server in an IPv4 network (steps of an IPv6 client accessing an IPv4 client are similar in principle, and are not described herein, and the same in embodiment 2), where a domain name of the IPv6 client is "www.IPv6.com", and a domain name of the IPv4 server is "www.IPv4.com". The whole communication process is as follows:

step S301: the IPv6 client initiates access to the IPv4 server by using the domain name www.IPv4.com of the IPv6 server, and the IPv6 client firstly sends an RR type (resource type) of 'AAAA' record query to a DNS6 domain name server to query a domain name www.IPv4.com.

Step S302: domain name server DNS6 does not have a resource record corresponding to domain name www.IPv4.com, and then initiates an RR type "AAAA" record query request to the SDN controller.

Step S303: and the SDN controller calls a domain name resolution management module, and the domain name resolution management module inquires the sent records without corresponding resource records.

Step S304: the domain name resolution management module converts the sent 'AAAA' into an 'A' record query request and then sends the record query request to a domain name server DNS4 in the IPv4 network.

Step S305: the DNS4 receives the record query request from the SDN controller, finds www.IPv4.com that it is a server in its own network, and replies an "a" record query response carrying the IPv4 address generated by the DNS4 to the SDN controller.

Step S306: after receiving the reply from the DNS4, the SDN controller translates the received "a" record query response into a corresponding "AAAA" query response, and translates the IPv4 address carried therein into a corresponding IPv6 address according to a corresponding rule, and returns the IPv6 address to the DNS6 (the address of the IPv4 is converted into the address of the IPv6 according to the existing rule, which is not described herein again).

Step S307: after receiving the reply of the SDN controller, the DNS6 replies the received query response to the IPv6 client.

Step S308: after receiving the reply of the DNS6, the IPv6 client sends a first data packet in an IPv6 format to the IPv4 server by using the IPv6 address in the reply message as a destination address.

Step S309: the SDN switch receives a first data packet in a communication IPv6 format from an IPv6 client to an IPv4 server, finds that a destination address of the first data packet is an IPv4 mapping address, the SDN controller calls an address management and mapping module, inquires whether a source IPv6 address has a mapping relation in an address translation table, if not, selects an idle address from an IPv4 address pool to the source IPv6 address, converts the idle address into an IPv4 address serving as a new source address, establishes the mapping relation, and converts the destination address into the IPv4 address according to corresponding rules. And finally, the network layer protocol conversion module translates the first data packet in the IPv6 format into the first data packet in the IPv4 format and sends the first data packet to the IPv4 server.

Step S310: and after receiving the first data packet, the IPv4 server replies a second data packet in an IPv4 format to the IPv6 client.

Step S311: after receiving the reply IPv4 format second data packet of the IPv4 server, the SDN switch finds that the destination address is an IPv6 mapped address, and then the SDN switch calls a network layer protocol conversion module, converts the address into an IPv6 address according to the address mapping relationship, and meanwhile queries the corresponding IPv6 address in an address conversion table by using the source IPv4 address.

Step S312: and finally, the network layer protocol conversion module translates the second data packet in the IPv4 format into a second data packet in the IPv6 format, and sends the translated and converted second data packet in the IPv6 format to the IPv6 client.

Example 2

As shown in fig. 4, the present embodiment discloses a communication method for accessing a server in an IPv4 network by using a client in an IPv6 network as an initiating host, where the domain name of the IPv4 client is "www.IPv4.com" and the domain name of the IPv4 server is "www.IPv6.com". The whole communication process is as follows:

step S401: the IPv4 client initiates access to the IPv6 server by using the domain name www.IPv6.com of the IPv4 server, and the IPv4 client firstly sends an RR type "A" record query to a DNS4 domain name server to query a domain name www.IPv6.com.

Step S402: domain name server DNS4 does not have a resource record corresponding to domain name www.IPv6.com, and then initiates an RR type "a" record query request to the SDN controller.

Step S403: and the SDN controller calls a domain name resolution management module, and the domain name resolution management module inquires the sent records without corresponding resource records.

Step S404: the domain name resolution management module then converts the sent 'A' into an 'AAAA' record query request and then sends the record query request to a domain name server DNS6 in the IPv6 network.

Step S405: the DNS6 receives the record query request from the SDN controller, finds www.IPv6.com that the record query request is a server in its own network, and replies an "AAAA" record query response carrying an IPv6 address generated by the DNS6 to the SDN controller.

Step S406: after receiving the reply from the DNS6, the SDN controller, in order to map the IPv6 address to the IPv4 address space, sends an address application request to the address management and mapping module, the address management and mapping module selects an available IPv4 address from the address pool and returns the address to the domain name resolution management module, and establishes an address binding relationship, and the domain name resolution management module synthesizes the received "AAAA" record query response into a corresponding "a" query response according to the returned address and returns the "a" query response to the DNS 4.

Step S407: after receiving the reply of the SDN controller, the DNS4 replies the received query response to the IPv4 client.

Step S408: after receiving the reply of the DNS4, the IPv4 client sends a first data packet in an IPv4 format to the IPv6 server by using the IPv4 address in the reply message as a destination address.

Step S409: the SDN switch receives a first data packet in a communication IPv4 format from an IPv4 client to an IPv6 server, finds that a destination address of the first data packet is an IPv6 mapping address, the SDN controller calls an address management and mapping module, and since the long address cannot be uniquely translated into the short address when the IPv6 address is converted into the IPv4 address, whether a mapping relation exists in a source IPv4 address is inquired in an address translation table, if not, a free address is selected from an IPv6 address pool to the source IPv4 address, a network layer protocol translation module converts the source address into an IPv6 address serving as a new source address, the mapping relation is established in the address translation table, and the destination address is converted into the IPv6 address according to corresponding rules. And finally, the network layer protocol conversion module translates the first data packet in the IPv4 format into the first data packet in the IPv6 format and sends the first data packet to the IPv6 server.

Step S410: and after receiving the first data packet in the IPv6 format, the IPv6 server replies a second data packet in the IPv6 format to the IPv4 client.

Step S411: after receiving the reply second data packet of the IPv6 server, the SDN switch finds that the destination address is an IPv4 mapped address, and then the SDN switch calls a network layer protocol conversion module, converts the address into an IPv4 address according to the address translation table mapping relationship, and meanwhile queries the corresponding IPv4 address in the address translation table by using the source IPv6 address.

Step S412: and finally, the network layer protocol conversion module translates the second data packet in the IPv6 format into a second data packet in the IPv4 format, and sends the translated and converted second data packet in the IPv4 format to the IPv4 client.

Example 3

As shown in fig. 1, the SDN-based IPv4 and IPv6 interconnection system provided in this embodiment includes:

the routing configuration submodule 101 realizes configuration of the border routing gateway device; the method mainly comprises the steps that a network administrator dynamically configures routing reachable information among networks in the network operation process, the network which can be reached by boundary routing gateway equipment directly connected with an edge switch is mainly configured, the network administrator adds and deletes the networks which can be reached by the boundary routing gateway according to the change of actual topology among the networks, and the configured routing reachable information among the networks only refers to logic information on a network layer;

the route detection submodule 102 realizes border route gateway device detection; when a network administrator configures network reachable information of a border routing gateway, a controller can actively detect the existence of the border routing gateway and physical information of the border routing gateway in an SDN network at the same time, the work is completed by a border routing detection module, the module can construct a detection message according to IP address information of the border routing gateway specified by the administrator in the SDN network, then the detection message is broadcasted on all edge switches, if the border routing gateway equipment exists, the detection message is responded, and the controller registers the equipment after receiving the response;

the routing management submodule 103 realizes maintenance management of information such as a routing table; after configuration and detection are respectively completed by a configuration submodule and a route detection submodule, a route management submodule adds network reachable information into a route forwarding table for maintenance and management, the whole system relates to two IP address types of IPv4 and IPv6, two route forwarding tables are established, the two address types are separately managed, then corresponding exit border route gateway equipment is inquired for a cross-network data packet according to the route forwarding table, a controller selects a path in an SDN network according to a switch connected with the exit border gateway equipment as two end points to issue a forwarding rule, and the data packet reaches a destination network through the path.

The domain name resolution management submodule 104 realizes proxy query and result conversion, and helps the client to obtain the address embedded with the destination address; the proxy query and result conversion can be carried out, the client is helped to obtain the address embedded into the destination address, and the resource servers requested by the IPv6 user comprise an IPv4 server and an IPv6 server. When a user client accesses the IPv6 server, a DNS 'AAAA' record query request is sent out, and the DNS64 server directly returns an IPv6 address; accessing the IPv4 server will also send out a DNS "AAAA" record query request, but the DNS6 server does not have a record, it is necessary to forward the request for converting the "AAAA" record into a "record to DNS4 for resolution, and then add a specified prefix to convert into a form of" AAAA "record and return it to the user client, the user client will receive an IPv6 address after initiating the DNS resolution request, the IPv6 address is calculated from the IPv4 address and the IPv6 prefix assigned to the NAT64 device, and the translation behavior follows the IP/ICMP translation algorithm defined in the RFC6145 standard. The resource servers requested by the IPv4 user include IPv4 servers and IPv6 servers. When a user client accesses the IPv4 server, a DNS 'A' record query request is sent out, and the DNS64 server directly returns an IPv4 address; accessing the IPv6 server will also send out a DNS "a" record query request, but the DNS4 server has no record, it needs to convert the "a" record request into an "AAAA" record request and forward the "AAAA" record request to the DNS6 for resolution, then request the network layer protocol translation module to allocate an available IPv4 address, establish a binding relationship in an address translation table, and convert the "AAAA" record into the form of an "a" record and return it to the user client, the user client will receive an IPv4 address after initiating the DNS resolution request, the IPv4 address is dynamically allocated by means of NAT or NAPT, and conforms to the general NAPT mapping rule RFC 3022.

The address management and mapping submodule 105 realizes the establishment of a dynamic management mapping relation between the IPv4 address and the IPv6 address in the DNS resolution phase;

the network layer protocol conversion sub-module 106 realizes protocol translation and address conversion between the IPv4 format data packet and the IPv6 format data packet in the data communication process; the method is mainly responsible for the mutual conversion of the headers of IPv4 and IPv6 format data packets and the translation of TCP, UDP and ICMP protocols at the fourth layer, and IP addresses and ports are changed in the conversion process. The translation behavior follows the IP/ICMP translation algorithm defined in the RFC6145 standard. The IPv4 address of the IPv4 server is translated into an IPv6 address according to the algorithm defined in RFC6052, and the mutual translation between the IPv6 address of the IPv6 host and the IPv4 address conforms to the common NAPT mapping rule RFC 3022. If the message is an ICMPv6/4 message, translating the Type, Code and Param fields in the message to obtain an ICMPv4/6 message, translating the embedded message header, and calculating the checksum of the ICMPv4/6 message; if the message is a TCP or UDP message, only the checksum of the TCP or UDP needs to be directly calculated.

The invention utilizes SDN technical means to realize the interconnection function of IPv4 and IPv6 in the control plane and the data plane in a software mode, and the mode does not need to change the existing network equipment of IPv4 and IPv6, thereby not only reducing the complexity of the network, but also having simple and convenient configuration. When the requirement of interconnection between the IPv4 and the IPv6 is not needed, only the interconnection modules of the IPv4 and the IPv6 are removed from the control plane and the data plane, and the influence on the network is very little.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. An SDN-based IPv4 and IPv6 interconnection method is characterized by comprising the following steps:

sending a first data packet in an IPv6/IPv4 format to the SDN by using the received IPv6/IPv4 address as a destination address through the IPv6/IPv4 client;

the IPv6/IPv4 client receives the second data packet.

2. The SDN-based IPv4 and IPv6 interworking method of claim 1, wherein the translation behavior complies with an IP/ICMP translation algorithm defined in RFC6145 standard; specifically, the IPv4 address is translated into the IPv6 address according to the algorithm defined in RFC 6052; the SDN calls a network layer protocol conversion module, and the IPv6/IPv4 format data packets are translated into IPv4/IPv6 format data packets, so that the general NAPT mapping rule RFC3022 is met.

3. The SDN-based IPv4 and IPv6 interworking method of claim 1, wherein the step of translating an IPv6 address into a corresponding IPv4 address is:

4. The SDN-based IPv4 and IPv6 interconnection method of claim 1, wherein a network layer protocol conversion module is invoked by the SDN to translate IPv6 format packets into IPv4 format packets, and the specific steps for sending to the IPv4 network are as follows:

5. The SDN-based IPv4 and IPv6 interconnection method of claim 1, wherein a network layer protocol conversion module is invoked by the SDN to translate IPv4 format packets into IPv6 format packets, and the specific steps for sending to the IPv6 network are as follows:

6. An IPv4 and IPv6 interconnection system based on an SDN is characterized by comprising an SDN controller, an SDN switch, a routing module and an interconnection module;

7. The SDN-based IPv4 and IPv6 interconnection system of claim 6, wherein the routing module, domain name resolution management submodule and address management and mapping submodule are installed and added to an SDN controller in a plug-in manner.