$4,2\mathrm{.}5$ points

$192\mathrm{.}169\mathrm{.}1\mathrm{.}1,10\mathrm{.}0\mathrm{.}0\mathrm{.}1,$ and $10\mathrm{.}0\mathrm{.}21\mathrm{.}1$ are all examples of:

IP addresses

Port numbers

Serial numbers

Computer identification numbers