Eventually we are all going to have to migrate on the Internet from IPv4 to IPv6. To be sure, this has taken longer than expected. But the sheer exhaustion of IPv4 addresses is bound to happen, and is a fundamental driver of the transition. So if you are a network programmer wondering about career trends, Stockebrand's book can be a useful consult.
He presupposes that you're already familiar with how IPv4 operates. You are then shown how IPv6 is much more powerful. Not just with the effectively infinite address space. But with how other drawbacks of IPv4 were addressed by the v6 designers. One of which is how v4 has no intrinsic Quality of Service. Current attempts to impose a QoS over v4 are crude and rather ad hoc. Whereas v6 has this built in as one of its fundamental properties.
Another v6 innovation is for Mobile IP, ie. nomadic computing. For this to be efficiently implemented, v4 falls short. But v6 gives a far simpler implementation. Thus Mobile IP may end up being one of the factors pushing for v6.