IPv6 over IPv4 tunneling

Implementation

IPv6 over IPv4 tunneling enables isolated IPv6 networks to communicate, as shown in Figure 76.


[NOTE: ]

NOTE:

The devices at the ends of an IPv6 over IPv4 tunnel must support the IPv4/IPv6 dual stack.


Figure 76: IPv6 over IPv4 tunnel

The IPv6 over IPv4 tunnel processes packets by using the following steps:

  1. A host in the IPv6 network sends an IPv6 packet to Device A at the tunnel source.

  2. After Device A receives the IPv6 packet, it processes the packet as follows:

    1. Searches the routing table to identify the outgoing interface for the IPv6 packet.

      The outgoing interface is the tunnel interface, so Device A knows that the packet needs to be forwarded through the tunnel.

    2. Encapsulates the IPv6 packet with an IPv4 header and forwards it through the physical interface of the tunnel.

      In the IPv4 header, the source IPv4 address is the IPv4 address of the tunnel source, and the destination IPv4 address is the IPv4 address of the tunnel destination.

  3. Upon receiving the packet, Device B de-encapsulates the packet.

  4. If the destination address of the IPv6 packet is itself, Device B forwards it to the upper-layer protocol. If not, Device B forwards it according to the routing table.

Tunnel modes

IPv6 over IPv4 tunnels include manually configured tunnels and automatic tunnels, depending on how the IPv4 address of the tunnel destination is acquired.

According to the way an IPv6 packet is encapsulated, IPv6 over IPv4 tunnels are divided into the following modes.

Table 11: IPv6 over IPv4 tunnel modes and key parameters

Tunnel type

Tunnel mode

Tunnel source/destination address

Destination IPv6 address format

Manually configured tunnel

IPv6 over IPv4 manual tunneling

The source and destination IPv4 addresses are manually configured.

Ordinary IPv6 address

Automatic tunnel

Automatic IPv4-compatible IPv6 tunneling

The source IPv4 address is manually configured. The destination IPv4 address is automatically obtained.

IPv4-compatible IPv6 address, in the format of ::IPv4-destination-address/96, where the IPv4-destination-address is the IPv4 address of the tunnel destination.

6to4 tunneling

The source IPv4 address is manually configured. The destination IPv4 address is automatically obtained.

6to4 address, in the format of 2002:IPv4-destination-address::/48, where the IPv4-destination-address is the IPv4 address of the tunnel destination.

ISATAP tunneling

The source IPv4 address is manually configured. The destination IPv4 address is automatically obtained.

ISATAP address, in the format of Prefix:0:5EFE:IPv4-destination-address/64 where the IPv4-destination-address is the IPv4 address of the tunnel destination.