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How to understand the tunnel technology in the IPv6 transition technology, I believe that many inexperienced people do not know what to do about it. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

Based on the rapid development of the Internet, the IPv4 address is about to be used up. IPv6 arises at the historic moment, and it has the advanced nature that IPv4 does not have, so it is imperative for IPv4 to transition to IPv6. However, because of the incompatibility between IPv6 and IPv4, the original IPv4 equipment needs to be replaced. In the dual-stack technology, the equipment used in the transition from IPv4 to IPv6 needs a large number of replacement, the cost in the process will be very huge, and the business running in the current network will also be interrupted, which is obviously not feasible. Therefore, the transition from IPv4 to IPv6 needs a gradual process. Under the premise that a large number of IPv4 networks have been deployed, at the initial stage of the transition, IPv6 networks are only "isolated islands" scattered all over the country. IPv6 over IPv4 tunnels make IPv6 messages transmitted in IPv4 networks through tunnel technology, thus realizing the island interconnection between IPv6 networks.

IPv6 over IPv4 tunnel

Tunnel technology is a kind of encapsulation technology based on IPv4 tunnel to transmit IPv6 data packets. The IPv6 packet is encapsulated in the IPv4 packet as unstructured data, so as to communicate through the IPv4 network, and the data packets can be encapsulated and de-encapsulated at both ends of the tunnel. A tunnel is a virtual point-to-point connection. By definition, tunneling technology refers to the whole process, including data encapsulation, transmission and unencapsulation.

Tunnel technology is an important means of transition from IPv6 to IPv4. The basic principles of IPv6 over IPv4 tunneling are shown below:

The realization of tunnel technology needs a starting point and an end point. The IPv4 address of the starting point of the IPv6 over IPv4 tunnel must be manually configured, and the end point can be determined by manual configuration and automatic acquisition. According to the way of obtaining the IPv4 address at the end of the tunnel, the IPv6 over IPv4 tunnel can be divided into manual tunnel and automatic tunnel.

Manual tunnel: that is, the border equipment can not automatically obtain the IPv4 address of the tunnel end point, so the IPv4 address of the tunnel end point needs to be manually configured before the message can be correctly sent to the tunnel end point. It is usually used in the router-to-router tunnel. The commonly used manual tunnel techniques are IPv6 over IPv4 manual tunnel and IPv6 over IPv4 GRE tunnel.

The above picture shows the manual tunnel encapsulation format of IPv6 over IPv4. The forwarding mechanism is as follows: when the IPv6 side of the tunnel boundary device receives an IPv6 message, it looks up the IPv6 routing forwarding table according to the destination address of the IPv6 message. If the message is forwarded from this virtual tunnel interface, it is encapsulated according to the IPv4 addresses of the tunnel source and destination configured by the tunnel interface. The original IPv6 message is transformed into an IPv4 message and handed over to the IPv4 protocol stack for processing. The message is forwarded to the end of the tunnel through the IPv4 network. After receiving a tunnel protocol message at the end of the tunnel, the tunnel is de-encapsulated. The unencapsulated message is handed over to IPv6 protocol stack for processing. Nodes that use manually configured tunneling to communicate with each other must have an available IPv4 connection, and must have at least one globally unique IPv4 address, each node must support IPv6, and the router needs to support dual protocol stacks, which fails when the tunnel passes through the NAT facility.

Using the standard GRE tunnel technology, IPv6 data packets are carried on the GRE tunnel of IPv4, providing point-to-point connection service, and there is a separate tunnel between the two points. GRE tunnel takes IPv6 as passenger protocol and GRE as bearer protocol, which does not limit the encapsulated protocol and transport protocol. The protocol encapsulated in a GRE tunnel can be any protocol allowed in the protocol (can be IPv4, IPv6, OSI, MPLS, etc.). The transport mechanism is the same as IPv6 over IPv4 manual tunneling.

Automatic tunneling: that is, the border device can automatically obtain the IPv4 address of the end point of the tunnel, so there is no need to configure the IPv4 address of the end point manually. The general practice is that the IPv6 address of the two interfaces of the tunnel is in the form of a special IPv6 address with embedded IPv4 address, so that the routing device can extract the IPv4 address from the destination IPv6 address in the IPv6 message. Automatic tunneling can be used between host to host or host to router. The commonly used automatic tunneling technologies are IPv4 compatible IPv6 automatic tunneling, 6to4 tunneling and ISATAP tunneling.

IPv4 is compatible with IPv6 automatic tunneling, and the destination address of the IPv6 message it carries (that is, the special address used for automatic tunneling) is the IPv4 compatible IPv6 address. The first 96 bits of IPv4 compatible IPv6 addresses are all 0, and the last 32 bits are IPv4 addresses. The following figure shows the IPv4-compatible IPv6 automatic tunnel forwarding mechanism.

The 6to4 tunnel is also an automatic tunnel, which is also established using the IPv4 address embedded in the IPv6 address, and is a specially configured relay route that allows it to communicate with the native IPv6 network. Tunneling can be used on a single host or on a local network, but nodes with 6 to 4 mechanism must have at least one globally unique IPv4 address, which is not conducive to interoperability between hosts that only support IPv4 and hosts that only support IPv6. The following figure is a schematic diagram of the 6to4 relay.

ISATAP tunneling is another automatic tunneling technology, which also uses a special IPv6 address form with embedded IPv4 addresses. Unlike 6to4, 6to4 uses IPv4 addresses as network prefixes, while ISATAP uses IPv4 addresses as interface identification, and regards IPv4 network as the data link layer of a non-broadcast multi-access network, so it does not need the underlying IPv4 network infrastructure to support multicast. The following figure shows an example of an ISATAP tunnel.

Through the tunnel technology, relying on the existing IPv4 facilities and requiring only the devices at both ends of the tunnel to support dual stacks, the interworking of multiple isolated IPv6 networks can be realized, but the tunnel configuration is more complex and does not support direct communication between IPv4 hosts and IPv6 hosts. However, as an application feature, IPv6 tunnel will play an important role in network transformation.

After reading the above, have you mastered how to understand the tunneling technology in the IPv6 transition technology? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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