Why transition to IPv6?

IPv4 supports up to 4 billion nodes only! (theoretical limit)
From address allocation efficiency, 100s of millions is the real upper limit
The limit is coming closer very quickly
Human population on the planet: 6 billion
IPv4 has to be re-engineered
Was designed in 1970s, has a lot of missing features

IPv6 expands IP address to 128bits
Supporting 3.4 x 10^38 nodes
Should be enough for my lifetime at least...
IPv6 incorporates recently-deployed technologies
Autoconfiguration and IPsec are mandatory
More friendly with mobilility/diffserv