5.5.4 Transition from IPv4 to IPv6—Dual Protocol Stack

5.5.4 Transition from IPv4 to IPv6—Dual Protocol Stack

Different from the software version update, the update of the IP protocol version cannot be completed in a short period of time, and only a gradual evolution method can be adopted. It can be interconnected and interoperable, so as not to affect the use of users. That is to say, the data between the host systems installed with the IPv6 protocol can use the IPv4 network to transmit, or support the communication between the IPv4 system and the IPv6 system. This requires a gradual transition from IPv4 to IPv6.

1. Transition from IPv4 to IPv6

There are mainly two methods

1. Dual stack , as the name implies, means that some hosts or routers in the network must install two protocol stacks at the same time, one IPv4 and one IPv6, before the protocol update is fully realized.

   as shown in the picture

   The protocol stack installed in the leftmost system only supports IPv4, and can generate and receive IPv4 datagrams. The rightmost system only supports IPv6, and can generate and process IPv6 datagrams. There is no direct communication between the two systems. Yes, there is a dual protocol stack system between the two, which supports both IPv4 and IPv6, and the task of Internet protocol conversion can be realized by using this system. For example, the IPv4 packets received from the leftmost system undergo protocol conversion to generate packets that the right system can recognize and process IPv6, so as to realize communication and information exchange between systems of different protocol versions.

   • How to use the system's IPv4 network to transmit data between two hosts with IPv6 protocol stack installed? How to use dual protocol stack? as the picture shows

     

     In the figure, A and F are two hosts, both of which are installed with IPv6 protocol stacks. The communication between these two remote hosts must pass through the intermediate IPv4 network. B and E are two access routers in the IPv4 network. In order to use the intermediate IPv4 The network implements information exchange between A and F, and dual protocol stacks must be deployed on B and E to support the access of A and F.

     The specific process is that host A generates an IPv6 datagram, the destination address filled in the header is F, the datagram first arrives at router B, and B uses the IPv6 protocol specification to parse the packet and convert it into a corresponding IPv4 packet, so that this packet can be directly Forwarding and processing in IPv4 network. After being forwarded by C and D, it reaches E, and host E converts the packet into a corresponding IPv6 message through reverse protocol conversion, and then sends it to host F.

     During the entire transmission process, the protocol conversion is realized through the dual protocol stack structure on B and E, and the remote communication between two IPv6 hosts using the IPv4 network is realized.

     The disadvantages brought by this method of using dual protocol stack conversion are welcome to participate in the discussion in the discussion area.

2. tunnel technology

   In addition to using dual protocol stacks for Internet protocol conversion, we can also use tunneling technology to realize the transition from IPv4 to IPv6. Tunnel technology is not unfamiliar to us because tunnel technology is widely used in the actual Internet environment. For example, the virtual private network (VPN) we discussed earlier ( 5.4.1 Virtual Private Network VPN ) uses tunnel technology to support secure remote communication between the internal networks of enterprises, then the problem before us is how to use tunneling technology to realize the transition from IPv4 to IPv6.

   as shown in the picture

   

   Similarly, A and F install the IPv6 protocol stack, and they use the IPv4 network for remote communication. Host A generates an IPv6 datagram, and the destination address filled in the header is F. The datagram arrives at router B first, and B no longer performs Internet Protocol conversion. , but encapsulates the IPv6 message generated by A as the data part into the data part of a new IPv4 datagram, the source IP address in the header of the outer IPv4 datagram is B, and the destination IP address is E, both of which are IPv4 networks The encapsulation process is called tunnel encapsulation . The IPv4 datagram formed after encapsulation is transmitted in the IPv4 network until it reaches router E. During this process, all intermediate routers in the IPv4 network will not process internal In other words, the IP datagrams exchanged between hosts A and F are invisible to the IPv4 network. On the router E, the internal IPv6 packet is taken out from the IPv4 packet, and delivered to the destination host F directly. This transfer process is declared over.

   From the entire data transmission process, we can see that although the dual protocol stack structure is installed on routers B and E by using tunnel technology, it does not realize the transformation of the protocol message format, but uses the encapsulation technology to shield the protocol and The difference between protocols protects the integrity of the original data information.