A DHCP server defines a scope, or range, of IP addresses that it uses to serve devices with an address. This pool of addresses is the only way a device obtains a valid network connection.

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This is another reason DHCP is so useful. DHCP allows several devices to connect to a network over a period of time without needing a pool of available addresses. For example, if 20 addresses are defined by the DHCP server, 30, 50, 200, or more devices can connect to the network as long as no more than 20 devices use one of the available IP addresses simultaneously.

Because DHCP assigns IP addresses for a specific period of time (called a lease period), using commands like ipconfig to find a computer's IP address yields different results over time.

Though DHCP is used to deliver dynamic IP addresses to its clients, it doesn't mean static IP addresses can't also be used at the same time. A mixture of devices that get dynamic addresses and devices that have their IP addresses manually assigned to them, can both exist on the same network.

ISPs use DHCP to assign IP addresses. This can be seen when identifying your public IP address. It will likely change over time unless your home network has a static IP address, which is usually only the case for businesses that have publicly accessible web services.
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