IPv6 transition strategy

There's no flag day, we will transition gradually

IPv4/v6 dual stack
Ethernet protocol type is different - they can coexist
IPv4/v6 dual stack node can speak with IPv4-only node
You can even use NAT for IPv4 communication
NAT network for IPv4, global network access for IPv6
Gradually IPv6 will become dominating

Tunnelling
At this moment, internet infrastructure uses IPv4
Tunnel IPv6 packet into IPv4

RFC2893 defines IPv6-over-IPv4 tunnelling
Can be used just like IPv6 p2p link
We run IPv6 routing protocol on top of it
+------------+            +------------+
|IPv6 network|============|IPv6 network|
+------------+ v6-over-v4 +------------+