Who could have guessed that 4.3 billion Internet connections wouldn’t be enough?

Certainly not Vint Cerf.

In 1976, Mr. Cerf and his colleagues in the R.& D. office of the Defense Department had to make a judgment call: how much network address space should they allocate to an experiment connecting computers in an advanced data network?

They debated the question for more than a year. Finally, with a deadline looming, Mr. Cerf decided on a number  4.3 billion separate network addresses, each one representing a connected device  that seemed to provide more room to grow than his experiment would ever require, far more, in fact, than he could ever imagine needing. And so he was comfortable rejecting the even larger number of addresses that some on his team had argued for.

“It was 1977,” Mr. Cerf said, in an interview last week. “We thought we were doing an experiment.”

“The problem was, the experiment never ended,” added Mr. Cerf, who is a former chairman of the Internet Corporation for Assigned Names and Numbers, or Icann, a nonprofit corporation that coordinates the Internet naming system. “We had no idea it would turn into the world’s global communications network.”