IP addressing

Answer

IPv4 uses 32 bits, written as four numbers, giving about 4 billion addresses — which ran out. IPv6 uses 128 bits, written as groups of hex digits, so the supply is effectively unlimited.

Answer

A public address is unique across the whole internet and reachable from anywhere on it, which makes it scarce. A private address is used inside one network only and is not routable on the internet, so millions of networks can reuse the same one.

Answer

The router swaps each device's private address for the organisation's one public address on the way out, remembers which device asked, and swaps it back on the reply. It exists because public IPv4 addresses are scarce.

Answer

A static address never changes, which anything that must always be findable needs — a web server, for instance. A dynamic address is assigned by DHCP when a device joins and may differ next time, which suits laptops and phones and reuses addresses efficiently.

Answer

Private addresses are not routable on the internet, so nothing outside can address an internal machine directly — it can only reply to a conversation that machine started. A firewall is still needed as well.