IPv6 tunneling

IPv6 Tunneling is the act of tunneling IPv6 packets from an IPv6 network through an IPv4 network to another IPv6 network. This is different than Network Address Translation (NAT) because once the packet reaches its final destination the true originating address of the sender will still be readable. The IPv6 packets are encapsulated within packets with IPv4 headers, which carry their IPv6 payload through the IPv4 network. This type of configuration is more appropriate for those who have completely transitional over to IPv6, but need an Internet connection, which is still mostly IPv4 addresses.

The key to IPv6 tunneling is the ability of the 2 devices, whether they are a host or a network device, to be dual stack compatible. They have to be able to work with both IPv4 and IPv6 at the same time. In the process the entry node of the tunnel portion of the path will create an encapsulating IPv4 header and transmit the encapsulated packet. The exit node at the end of the tunnel receives the encapsulated packet. The IPv4 header is removed. The IPv6 header is updated and the IPv6 packet is processed.

There are two types of tunnels in IPv6:

Automatic tunnels	Automatic tunnels are configured by using IPv4 address information embedded in an IPv6 address – the IPv6 address of the destination host includes information about which IPv4 address the packet should be tunneled to.
Configured tunnels	Configured tunnels must be configured manually. These tunnels are used when using IPv6 addresses that do not have any embedded IPv4 information. The IPv6 and IPv4 addresses of the endpoints of the tunnel must be specified.

Tunnel configurations

There are a few ways in which the tunneling can be performed depending on which segment of the path between the end points of the session the encapsulation takes place.

Network Device to Network Device	Dual stack capable devices connected by an IPv4 infrastructure can tunnel IPv6 packets between themselves. In this case, the tunnel spans one segment of the path taken by the IPv6 packets.
Host to Network Device	Dual stack capable hosts can tunnel IPv6 packets to an intermediary IPv6 or IPv4 network device that is reachable through an IPv4 infrastructure. This type of tunnel spans the first segment of the path taken by the IPv6 packets.
Host to Host	Dual stack capable hosts that are interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves. In this case, the tunnel spans the entire path taken by the IPv6 packets.
Network Device to Host	Dual stack capable network devices can tunnel IPv6 packets to their final destination IPv6 or IPv4 host. This tunnel spans only the last segment of the path taken by the IPv6 packets.

Regardless of whether the tunnel starts at a host or a network device, the node that does the encapsulation needs to maintain soft state information, such as the maximum transmission unit (MTU), about each tunnel in order to process the IPv6 packets.

Use the following command to tunnel IPv6 traffic over an IPv4 network. The IPv6 interface is configured under config system interface. The command to do the reverse is config system ipv6-tunnel. These commands are not available in transparent mode.

config system sit-tunnel

edit <tunnel name>

set destination <tunnel _address>

set interface <name>

set ip6 <address_ipv6>

set source <address_ipv4>

end

Variable	Description	Default
edit <tunnel_name>	Enter a name for the IPv6 tunnel.	No default.
destination <tunnel_address>	The destination IPv4 address for this tunnel.	0.0.0.0
interface <name>	The interface used to send and receive traffic for this tunnel.	No default.
ip6 <address_ipv6>	The IPv6 address for this tunnel.	No default.
source <address_ipv4>	The source IPv4 address for this tunnel.	0.0.0.0