What is the difference between a Static IP Address and a Dynamic IP Address?

Two terms commonly used in IP networking are static addressing, and dynamic addressing.

A host with a static IP address has a fixed IP address. Static. Unchanging. Always the same. Usually manually configured, though it is possible to configure a DHCP server to always provide the same IP address.

A dynamic IP is a variable or changeable IP address. Dynamic. Variable. The assigned IP address can change hourly, daily, monthly, when your gateway-firewall-router-modem device is power-cycled, or evem sometimes (but not with any certainty) not at all. Details here vary. Dynamic addresses are typically assigned by a DHCP server from a pool of available IP addresses, though it is possible for hosts to self-assign IP addresses from specific IP address ranges when there is no DHCP server.

OS X Server — which is OS X with the Server.app installed — and OpenVMS most other server-oriented hosts will generally want a static IP address; a fixed and unchanging IP address.

OS X clients and most other client-oriented systems will accept dynamic IP addresses, and are generally configured to ask for a dynamic address. Client systems can accept and can use whatever IP address the DHCP server passes out. Using DHCP and dynamic addresses makes for far more efficient use of the available IP address space, particularly when mobile devices are in use.

The discussion of static and dynamic IP usually arises in the context of an ISP network connection. Residential ISP connections are usually dynamic addresses; the IP addresses are DHCP issued, and variable addresses. Secondary to this, ISPs variously also implement firewalls that block certain network activity from dynamic IP addresses; server-oriented network protocols can be blocked from the ISP residential dynamic IP service tier, and running web servers or mail servers are variously disallowed by the terms of service.

ISP static IP connections generally allow running servers, generally lack firewall blocks at the ISP, and the static IP address also means that DNS-based network checks will succeed; that other hosts will accept a mail server operating in the configuration, where other mail servers will often be configured to reject mail arriving from a mail server with a dynamic IP address. (Yes, it is possible for other hosts to determine this remotely.)

For More Information

In addition to the Index: Mac OS X Server and Client Networking topic index, here are some of the following topics here at HoffmanLabs may be interesting to readers of this article:

And definitely check for your ISP terms of service, regardless.