WB1 9.30 Automatic 6to4 Tunneling

9.30 Automatic 6to4 Tunneling

• Using the IPv4 Loopback 0 interfaces create automatic 6to4 tunnels
connecting R3, R4, and R5.
• Create additional Loopback interfaces on every router with the subnet
number 0 and the prefix length of 64 under the respective 6to4 /48 prefix.
• Use static routing to obtain connectivity between the newly allocated
subnets.

---------------------------

R3:
interface Tunnel 345
tunnel source Loopback0
tunnel mode ipv6ip 6to4
ipv6 address 2002:9601:303::3/64
!
ipv6 route 2002::/16 Tunnel 345
!
interface Loopback200
ipv6 address 2002:9601:303:1::3/64

R4:
interface Tunnel 345
tunnel source Loopback0
tunnel mode ipv6ip 6to4
ipv6 address 2002:9601:404::5/64
!
ipv6 route 2002::/16 Tunnel 345
!
interface Loopback200
ipv6 address 2002:9601:404:1::4/64

R5:
interface Tunnel 345
tunnel source Loopback0
tunnel mode ipv6ip 6to4
ipv6 address 2002:9601:505::5/64
!
ipv6 route 2002::/16 Tunnel 345
!
interface Loopback200
ipv6 address 2002:9601:505:1::5/64

-----------------------------

Automatic 6to4 tunnels are multipoint by design. The idea is to allow automatic
routing across an IPv4 cloud based on a part of the destinations IPv6 address.
Specifically, the format of the 6to4 IPv6 address is as follows:

2002 (16 bits):IPv4 address (32 bits):Subnet ID(16 bits):Interface ID (64 bits)

When a packet is routed across the 6to4 tunnel, the router extracts the IPv4
address embedded in the IPv6 address and uses it to build the IPv4 destination
address of the tunnel header. The receiving router strips the header, extracts the
IPv6 packet, and routes it based on the IPv6 routing table.

As you can imagine, 6to4 subnets have some addressing restrictions. First, you
need to use the 16-bit prefix 2002, as it is the common reservation for all 6to4
deployments. Second, you need to select the public IPv4 address used to create
the /48 prefix. It is common to pick any interface of the border router and then
allocate the /64 subnets to other devices on the network, as long as the address
is publicly routable.

6to4 tunnels are a transition mechanism for hosts that do not have native IPv6
connectivity, allowing them to reach other nodes that have full connectivity to the
IPv6 Internet. Due to the multipoint nature of the 6to4 tunnels, only static routing
is possible with this technology. However, it is common to simply route the whole
2002::/16 prefix to the 6to4 tunnel.

In our case, the use of Loopback 0 subnets results in the following IPv6 6to4
prefixes:

R3: 150.1.3.3 = 2002:9601:303::/48
R4: 150.1.4.4 = 2002:9601:404::/48
R5: 150.1.5.5 = 2002:9601:505::/48

“9601” in hex corresponds to “150.1” in decimal, and on R3 “303” corresponds to
“3.3”.

-----------------------------

Rack1R5#show interfaces tunnel 345
Rack1R5#ping ipv6 2002:9601:404:1::4
Rack1R5#ping ipv6 2002:9601:303:1::3