This blog series was recommended by another of our awesome students and IEOC community members, Marcio A. Costa.
In the first part of this series, we will look at the Manual IPv6 tunnels that are simple to create in order to connect two “islands” of IPv6 separated by IPv4-only devices. For this blog, we will use the following simple topology:

Let us pretend that the R2 device is not capable of IPv6. How can we connect the islands of IPv6? Well, one option is the manual IPv6 tunnel. This is for stable connections that might require regular communication between two edge routers. To create this tunnel, you assign an IPv6 address to the tunnel, and you use the IPv4 addresses for tunnel source and destination. Obviously, the routers forming the tunnel must support IPv6 and IPv4. But remember, the IPv4-only devices in the middle are passing IPv4-looking packets, so they are just fine.
I have configured the topology above for us. EIGRP is ensuring all IPv4 addresses are reachable. I have also created the loopbacks and the islands of IPv6. We begin our configurations by enabling RIP for IPv6 (RIP Next Generation;RIPng) on the loopbacks:

R1(config)#ipv6 unicast-routing
R1(config)#interface loopback 0
R1(config-if)#ipv6 rip CCIERIP enable
R1(config-if)#end

R3(config)#ipv6 unicast-routing
R3(config)#interface loopback 0
R3(config-if)#ipv6 rip CCIERIP enable
R3(config-if)#end

So now we have real islands of IPv6. There is no chance for connectivity between these networks since RIPng is not running on the interfaces facing R2, nor is RIPng running anywhere on R2.
It is time now to create the manual IPv6 tunnel. If we run RIPng on the tunnel, we should have dynamic routing across the IPv4-only device and full IPv6 connectivity! Here we go:

R1(config)#interface tunnel 0
R1(config-if)#ipv6 address 2001:13::1/64
R1(config-if)#tunnel source fastethernet0/0
R1(config-if)#tunnel destination 10.20.20.3
R1(config-if)#tunnel mode ipv6ip
R1(config-if)#ipv6 rip CCIERIP enable
R1(config-if)#end

R3(config)#interface tunnel 0
R3(config-if)#ipv6 address 2001:13::3/64
R3(config-if)#tunnel source fastethernet0/0
R3(config-if)#tunnel destination 10.10.10.1
R3(config-if)#tunnel mode ipv6ip
R3(config-if)#ipv6 rip CCIERIP enable
R3(config-if)#end

Now it is time for verification (drumroll please!). Here, the obvious most efficient verification is a simple IPv6 ping from R1 to the remote IPv6 island on R3.

R1#ping 2001:3::3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:3::3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/10/16 ms
R1#

Excellent!We will investigate another transition option in the next part of this series. Thanks for tuning in! If you want more training targeted at this subject, check out any CCIE R&S product! You should have your Tier 1 understanding of this feature now, so you should target Tier 2 or Tier 3 products. Tier 2 would be workbook practice, while Tier 3 would be Poly-labs or Graded Mock Labs.