IPv6 network transition technology

In order to better integrate IPv4 and IPv6 protocols, we have adopted many technologies for intercommunication between the two networks. First, let's introduce the tunneling technology. And some related transitional technologies.

Tunneling Technology

Before an IPv6 network completely replaces an IPv4 network, some access network technologies first have an IPv6 protocol stack. Generally, in the early stage of transition, we often compare these networks to IPv6 islands in the IPv4 ocean. The transition problems can be divided into two categories: the first category is to solve the communication problems between these IPv6 islands; the second type is to solve the problem of communication between the IPv6 Island and the IPv4 ocean ｡

The purpose of IPv6/IPv4 tunneling technology is to use existing IPv4 facilities to serve IPv6 hosts, this allows scattered IPv6 "isolated islands" to communicate with each other across IPv4 networks. When IPv6 packets pass through IPv4 networks, no matter which tunnel mechanism uses a "packet-Unpacking" process, that is, the tunnel endpoint at the sending end encapsulates the IPv6 packet in an IPv4 packet, regards the IPv6 packet as IPv4 load data, and sets the protocol field of the IPv4 packet to 41, it indicates that the load of the IPv4 packet is an IPv6 encapsulation package, and then the package is transmitted on the IPv4 network. When the IPv4 encapsulation package marked as 41 in the protocol field reaches the Tunnel endpoint at the receiving end, this endpoint removes the IPv4 header of the package and takes out the IPv6 package for further processing. How to Determine the Source and Destination addresses of the IPv4 package during IPv4 encapsulation is a key issue of encapsulation, the main difference between the existing IPv4/IPv6 Tunneling mechanism is how to determine the IPv4 packet address ｡

Configure tunnel manually

Configuring the Tunnel manually is an end-to-end mechanism. The administrators at both ends of the Tunnel need to work together to establish the Tunnel. When the administrator configures both ends of the Tunnel, first, you should specify the IPv4 addresses at both ends of the tunnel interface to encapsulate all IPv6 packets transmitted in this tunnel, the source and destination IPv4 addresses must be extracted from the configuration information. Second, the Administrator must set the required route information to determine which IPv6 packets need to be transmitted through a tunnel ｡

Because Manual Tunnel Configuration is the first transition mechanism supported by IPv6, it is widely supported at present. This mechanism does not require the IPv6 address of the host using the tunnel to contain some fixed information, however, the IPv6 address and IPv4 address at both ends of the tunnel must be negotiated and set in advance to complete the tunnel configuration at both ends, this puts a huge burden on the Technical Management Personnel of the access network. Manual configuration requires a large workload (tens of thousands of tunnels are processed every day), resulting in low efficiency and prone to errors ｡

In order to simplify the workload of establishing a tunnel, especially the workload of the tunnel server, the tunnel proxy model is proposed. The tunnel proxy system provides a mechanism to simplify the tunnel configuration, it can reduce heavy tunnel configuration work. The idea of tunnel proxy is to provide a dedicated server as the tunnel proxy, automatically manage the tunnel requests sent by users. The user can establish a tunnel connection with the IPv6 protocol network through the tunnel proxy, to access available external IPv6 resources. The tunnel proxy transition mechanism attracts more IPv6 users in the early stages of IPv6, enabling them to conveniently and quickly implement IPv6 connections through the IPv4/IPv6 Tunneling mechanism, it also provides a simple and quick access method for early IPv6 providers ｡

Automatic Tunnel Configuration

Automatic Tunnel configuration requires a static bidirectional Tunnel, and the channel side does not need to work with other parties. The system creates a Tunnel interface or contains IPv4 address information in the IPv6 address, in this way, when the tunnel encapsulates an IPv6 packet, you can extract the IPv4 address from the IPv6 address and fill in the IPv4 header. Alternatively, you can provide an IPv4 addressing mode, use addressing technology to obtain the IPv4 address of the Peer end. Currently, there are 5 common automatic tunneling technologies ｡

◆ Automatic tunnel technology using IPv4 compatible addresses: Automatic tunnel can complete point-to-point connections, the Manual Tunnel is only a point-to-point connection. IPv4 is compatible with the IPv6 automatic tunnel technology to automatically generate tunnels. We know that a tunnel requires a start point and an end point, after the start and end points are determined, the tunnel can be determined. In the IPv4-compatible IPv6 automatic tunnel, we only need to tell the device tunnel start point, the tunnel endpoint is automatically generated by the device. To enable the device to automatically generate an endpoint, an IPv4-compatible IPv6 tunnel must use a special address: IPv4-compatible IPv6 address ｡

◆ 6over4 technology: IPv4 multicast mechanism is used to implement virtual links and automatically establish a tunnel mechanism. interfaces using this mechanism are addressed using the ND (Neighbor Discovery) protocol proposed in RFC2461, when an IPv6 packet needs to be encapsulated, the IPv6 layer sends the ND request packet to address the destination IPv6 address. The 6over4 interface encapsulates the ND request packet into an IGMP header and then sends it to the IPv4 multicast domain; if another 6over4 interface in the multicast domain has the requested IPv6 address, the interface sends the ND response packet containing its IPv4 address in the same way, after receiving the ND response, the query interface can obtain the IPv4 address of the Target Interface ｡

◆ 6to4 technology: the 6to4 address must be used for interfaces using this mechanism. The prefix format is 2002: IPv4 Addr:/48. This mechanism requires the configuration of two types of routers, the two types of routers are: (1) 6to4 Router (6to4 Router). As an IPv6 domain egress Router, the outbound interface is 6to4; (2) the 6to4 Relay Router (6to4 Relay Router) serves as the 6to4 Router for Relay of multiple 6to4 Router. Generally, you can set the default route of 6to4 Router to a 6to4 Relay route, you can set route information in the relay router to connect multiple IPv6 domains ｡

◆ ISATAP (Intra-Site automation IC Tunnel Addressing Protocol) technology: it is an Intra-Site Automatic Tunnel Protocol. ISATAP server is used to assign an ISATAP prefix. The Intra-domain host obtains This prefix using the ISATAP interface, the prefix of the ISATAP address: 5EFE: IPv4 addr/64 ｡

◆ Teredo technology: Teredo is an Address Allocation and automatic IPv4/IPv6 Tunneling mechanism, IPv6 unicast connections can be achieved across IPv4 networks. It encapsulates IPv6 packets in UDP/IPv4 packets for transmission. It uses a special address format, except for a fixed Teredo prefix, the IPv4 address of the Teredo server, the public IPv4 address of the client, and the UDP port are also inserted into the IPv6 address ｡