What is the difference between a static and a dynamic IP address?
Whether your public address stays the same or changes periodically — and for most people it matters far less than it sounds, until it suddenly matters a great deal.
Dynamic. Your ISP assigns an address from a pool, and it may change — on reconnection, on router restart, after a line fault, or on a schedule. This is the default for residential broadband almost everywhere.
Why ISPs prefer it: addresses are a scarce resource, and a pool serves more subscribers than there are addresses, since not everyone is connected at once. It also discourages running servers on consumer lines, which is generally what the terms of service require.
In practice, dynamic addresses on modern broadband are frequently stable for months because the lease keeps renewing — so people assume they are static until one day they are not.
Static. A fixed address assigned permanently to your connection, usually an extra-cost option or bundled with business service.
When you genuinely need static:
Hosting anything reachable from outside — a mail server, VPN endpoint, game server or remote access.
IP allowlisting. If a client, a VPN, a payment gateway or a corporate system restricts access to specific addresses, a changing address breaks it.
Sending email directly, since reputation and reverse DNS attach to the address, and residential dynamic ranges are widely blocklisted for mail.
Some site-to-site VPN configurations.
When you do not. Ordinary browsing, streaming, gaming as a client, and remote access via a service that handles connectivity for you — all of which work fine on dynamic.
Dynamic DNS is the usual workaround. A small client on your network reports your current address to a DNS provider, which keeps a hostname pointed at it. Good enough for remote access and cameras, with a short gap after each change. It does not work behind CGNAT, which is the crucial limitation — if your ISP is sharing one address between customers, no amount of dynamic DNS helps.
Do not confuse this with a static LAN address, which is a local setting and unrelated. A DHCP reservation is usually better for that.
IPv6 changes the picture, since addresses are plentiful and prefixes are often stable.