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ThinkMo EDU Share – network 36.Communication mechanism and method between IPv6 and IPv4

蒂娜 No Comments 11/04/2022

ThinkMo EDU Share – network 36.Communication mechanism and method between IPv6 and IPv4

Background status

Although IPv6 has been considered as one of the core standards of the next-generation Internet protocol. However, it takes a process from birth to widespread application of new things, especially for the Internet which is still well supported by IPv4. Before IPv6 networks became popular all over the world, there were always some networks that first used the IPv6 protocol stack and hoped to be able to communicate normally with the current Internet.

In order to achieve this goal, researchers must develop IPv4/IPv6 interworking technology to ensure a smooth transition from IPv4 to IPv6. In addition, the interworking technology should be “seamless” for ordinary users, without any inconvenience to use. Efficient transfer of information.

During the transition period, the problems of mutual communication to be solved are nothing more than two categories:

The first category is the problem of communication between IPv6; the second category is to solve the communication problem between IPv6 and IPv4.

A lot of solutions have been proposed for these two types of problems, some of which are quite mature and have formed RFC (RequestForCommnets), and some are just as Internetdrafts and need to be further improved.

Transition technology

At present, there are mainly three basic technologies for solving the transition problem: dual-protocol stack (RFC2893obsoleteRFC1933), tunnel technology (RFC2893), and NAT-PT (RFC2766).

1.Dual Stack

The nodes using this technology run both IPv4 and IPv6 protocol stacks at the same time. This is the most direct way to keep IPv6 nodes compatible with pure IPv4 nodes, which are aimed at communicating end nodes (including hosts and routers). This approach provides full compatibility with IPv4 and IPv6, but does not help with the problem of IP address exhaustion. This approach increases the complexity of the network due to the need for a dual routing infrastructure.

2.Tunnel technology

Tunneling technology provides a method for transmitting IPv6 data using the existing IPv4 routing system: IPv6 packets are treated as data without structural significance, encapsulated in IPv4 datagrams, and transmitted by IPv4 networks. Depending on how they are established, tunnels can be divided into two categories: (manually) configured tunnels and automatically configured tunnels. The tunnel technology cleverly utilizes the existing IPv4 network. Its significance is to provide a method to enable IPv6 nodes to communicate during the transition period, but it cannot solve the problem of mutual communication between IPv6 nodes and IPv4 nodes.

3.Gateway translation (NAT-PT)

In addition to IPv4 address and IPv6 address translation, the translation gateway also includes protocol and translation. As an intermediate device of communication, the conversion gateway can convert the IP header address between IPv4 and IPv6 networks, and at the same time, perform corresponding semantic translation for packets according to different protocols, so as to enable transparent communication between pure IPv4 and pure IPv6 sites.

IPv6 communication

It refers to the communication between v6 and v6. The main methods are as follows:

1.Configured Tunnel

The establishment of such a tunnel is manually configured, and requires the cooperation of the administrators of the networks where the two endpoints of the tunnel are located. The endpoint address of the tunnel is determined by configuration, and there is no need to assign a special IPv6 address to the site. It is suitable for frequent communication between IPv6 sites. The encapsulation node of each tunnel must store the address of the tunnel end point. When an IPv6 packet is transmitted on the tunnel, the end point address will be encapsulated as the destination address of the IPv4 packet. Usually the encapsulating node decides whether a packet should be forwarded through the tunnel according to the routing information.

Sites that use manually configured tunnels for communication must have an available IPv4 connection and at least one globally unique IPv4 address. Every host in the site needs to support at least IPv6, and the router needs to support dual stack. This mechanism is not available where the tunnel is to go through a NAT facility.

The main disadvantage of manually configuring tunnels is that the network administrator is burdened with detailed configuration for each tunnel.

2.Auto-configured Tunnel

The establishment and dismantling of this kind of tunnel is dynamic, and its endpoint is determined according to the destination address of the packet, which is suitable for separate hosts or between sites that do not communicate frequently. The auto-configured tunnel requires sites to use IPv4-compatible IPv6 addresses. There must be an available IPv4 connection between these sites. Each host using this mechanism needs to have a globally unique IPv4 address.

Adopting this mechanism does not solve the problem of IPv4 address space exhaustion (sites using manually configured tunnels do not need IPv4 addresses). In addition, there is a danger that if all IPv4 routing tables on the Internet are included in the IPv6 network, the problem of routing table expansion will be aggravated. Both endpoints of such a tunnel must support dual stacks (manual configuration is not required). This mechanism is not available where the tunnel is to go through a NAT facility.

3.Tunnel Broker

TunnelBroker is not a tunnel mechanism, but a mechanism to facilitate tunnel construction. The configuration process of the tunnel can be simplified, and it is suitable for the case where a single host obtains an IPv6 connection. TunnelBroker can also be used between sites, but at this time, many entries may be introduced into the IPv6 routing table, which makes the IPv6 routing table too large and goes against the original intention of IPv6 design. Users can obtain persistent IPv6 addresses and domain names from ISPs that support IPv6 through TunnelBroker.

TunnelBroker requires that both sides of the tunnel support dual stack and have available IPv4 connection, which is not available when the tunnel has to go through a NAT facility. By adopting the TB method, an IPv6 ISP can easily perform access control on users and allocate network resources according to policies.

TB conversion mechanisms include TunnelServer (TS) and TunnelBroker (TB). The server and the boker are located on different computers, and the control of the tunnel is usually in the form of a web.

4.6 over 4

6over4 is a point-to-point, point-to-route, and route-to-point automatic tunneling technology that is used as a single-point or multi-point connection between IPv6 nodes through an IPv4 intranet. The IPv4 address of the tunnel endpoint is determined by the neighbor discovery method. Unlike manually configured tunnels, it does not require any address configuration; unlike automatic tunnels, it does not require the use of V4-compatible V6 addresses.

But the premise of adopting this mechanism is that the IPv4 network infrastructure supports IPv4 multicast. The IPv4 multicast domain here can be a network using a globally unique IPv4 address, or a part of a private IPv4 network. This mechanism applies to isolated IPv6 hosts on physical links not directly connected by IPv6 routers, enabling them to use IPv4 broadcast domains as their virtual links and become fully functional IPv6 sites. The basic principle is as follows:

5.6 to 4

6to4 is also an automatic tunneling mechanism that converts v4 to v6. This mechanism requires the site to use a special IPv6 address, which is automatically derived from the site’s IPv4 address. Therefore, each node using the 6to4 mechanism must at least have a globally unique IPv4 address (this address allocation method can enable border routers in other domains to automatically distinguish whether the tunnel receiving endpoint is in this domain).

Since the IPv4 address of the tunnel endpoint can be extracted from the IPv6 address under this mechanism, the establishment of the tunnel is automatic. 6to4 does not introduce new entries in the IPv4 routing table, but only adds an entry in the IPv6 routing table. IPv6 ISPs using the 6to4 mechanism only need to do very little management work, and this mechanism is very suitable for communication between sites running IPv6. 6to4 requires at least two routers in the tunnel to support dual stack and 6to4, and the host requires at least IPv6 protocol stack.

This mechanism treats the wide-area IPv4 network as a unicast point-to-point link layer. This mechanism is suitable as a conversion tool in the initial stage of V4/V6 coexistence. It can coexist with firewalls and NATs, but the NATbox must have a globally unique IPv4 address, and should have a 6to4 mechanism and complete routing functions. The principle in windows2003 is as follows:

IPv6/IPv4 communication

1.DualStack Model

Under this model, any node is fully dual-stacked. At this time, there is no mutual communication problem between IPv4 and IPv6, but this mechanism assigns an IPv4 address to each IPv6 site. This method cannot solve the problem of insufficient IPv4 address resources, and it will be difficult to be satisfied with the increase of IPv6 sites, so this method can only be used in the early transition process.

2.LimitedDual Stack Model

Under this model, the server and router are still dual-stacked, and hosts that are not servers only need to support IPv6. This mechanism can save a lot of IPv4 addresses, but there will be problems in the communication between pure IPv6 and pure IPv4 nodes, in order to solve this problem, it must be combined with other technologies.

3.SIIT (Stateless IP/ICMP Translation)

SIIT defines a method for translating between IPv4 and IPv6 packet headers. This translation is stateless and therefore must be translated for every packet. This mechanism can be combined with other mechanisms (such as NAT-PT) for communication between pure IPv6 sites and pure IPv4 sites, but this technology is not available in environments that use network layer encryption and data integrity protection.

A pure IPv6 node communicates with a pure IPv4 node through a SIIT translator. An IPv6 node sees each other as a host with an IPv4mapped address, while itself uses an IPv4translated address. If the destination address in the IP packet sent by the IPv6 host is an IPv4 mapped address, then the SIIT converter knows that the IP packet needs to be converted by protocol.

4.NAT-PT (Network Address Translation-Protocol Translation)

NAT-PT is to perform header and semantic translation (PT) between IPv4 packets and IPv6 packets while doing IPv4/IPv6 address translation (NAT). Suitable for communication between pure IPv4 sites and pure IPv6 sites. For some high-level protocols (such as FTP) with embedded address information, NAT-PT needs to cooperate with the gateway of the application layer to complete the translation. Using port information on the basis of NAT-PT, NAT-PT can be implemented, which is not fundamentally different from the current NAT-PT under IPv4.

This mechanism is suitable for the initial stage of transition, so that hosts based on dual protocol stacks can run IPv4 applications and communicate with each other with IPv6 applications. This technique allows applications that do not support IPv6 to transparently access pure IPv6 sites. This mechanism requires that the host must be dual-stacked, and three special extension modules must be inserted into the protocol stack: domain name resolver, address mapper and translator, which is equivalent to using NAT-PT in the host’s protocol stack.

5.BIA (Bump-In-the-API, Internet Draft)

This technology is similar to BIS, except that the translation of packets is performed at the API layer rather than at the protocol stack level, so its implementation is simpler than that of BIS, because it does not need to translate IP packet headers. The main difference between BIS and BIA is: BIS is used on systems without IPv6 protocol stack, and BIA is used on systems with IPv6 protocol stack.

When the IPv4 application on the dual-stack host communicates with other IPv6 hosts, the API translator detects the socketAPI-based function sent from the IPv4 application, and calls the IPv6 socketAPI function to communicate with the IPv6 host.

In addition to the above seven communication methods, IPv6 and IPv4 can also communicate through TRT, DSTM, ALG and other methods. Due to space constraints, it will not be introduced.

Transition Mechanism

It can be seen from the existing transition mechanism that all the current schemes are proposed for a certain kind of problem. These transition mechanisms are not universally applicable, each mechanism is suitable for one or several specific network situations, and often needs to be used in combination with other technologies. In practical application, various practical situations need to be comprehensively considered to formulate an appropriate transition strategy. For a certain type of interconnection problem, designers can find new ways, and continue to improve and update this way with network technology and development.

In order to choose an appropriate mechanism, the type of application, scope and type of system should be identified first, and then an appropriate transformation mechanism should be selected for design and implementation.

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