Overview IPv6 Tunnel

IPv6 (IPv4 over IPv6 / IPv6 over IPv6) tunnel is one of many tunnel technologies, which is similar to GRE (generic routing Encapsulation (general routing package) tunnel, the beginning and end of the tunnel need to be manually configured. It is a virtual point-to-point connection, which provides a transmission channel for the encapsulated packet. The two ends of the tunnel separately encapsulate and de-encapsulate the packet. IPv6 Tunnel can encapsulate both IPv4 data packets and IPv6 packets, so that these encapsulated packets can be transmitted in IPv6 network. When the packet is IPv4 packet, it is called IPv4 over IPv6 Tunnel. When the data packet is IPv6 packet, it is called IPv6 over IPv6 Tunnel. If the packet is not distinguished from IPv4 packet or IPv6 packet, it is called IPv6 Tunnel.

• IPv4 over IPv6/IPv6 over IPv6 tunnel + encapsulation

When IPv6 / IPv4 packet is to be sent through IPv6 Tunnel, the tunnel adds an IPv6 packet header in its header, the protocol number in the IPv6 packet header is set to 4, the source address in the IPv6 packet header is set to the source address of the tunnel, and the destination address in the IPv6 packet header is set to the address of the tunnel.

• IPv4 over IPv6/IPv6 over IPv6 packet structure

IP / IPv6 payload: the IP/IPv6 packet load before entering the tunnel as the payload of the tunnel packet.

IP / IPv6 header: the IP / IPv6 packet header before entering the tunnel.

Outer IPv6 header: the encapsulated external IP packet header, which is a transmission tool to realize IP / IPv6 packet passing through IPv6 network.

• IPv4 over IPv6/IPv6 over IPv6 packet forwarding

After the packets are encapsulated at the starting point of IPv4 over IPv6 / IPv6 over IPv6 Tunnel, they are routed according to the encapsulated destination address, and then sent out from the corresponding network interface. The intermediate equipment forwards it as a common IPv6 packet until the packet reaches the end of the tunnel.

• IPv4 over IPv6/IPv6 over IPv6 de-capsulation

The de-capsulation process is opposite to the encapsulation process. After receiving the packet, the end of the tunnel first analyzes the outer IP header. If the destination address is its own address, check the protocol field of the IPv6 packet header. If the protocol field is 41, the packet will be sent to the IPv4 over IPv6/IPv6 over IPv6 Tunnel for processing. After the out IPv6 header of the packet is removed from the tunnel, the route is selected according to the destination address of the de-capsulated packet, and the subsequent processing is carried out according to the route selection result.