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What Is DHCP? A Beginner's Guide

See, step by step, how a device automatically gets an IP address.

  1. What Is DHCP?

    DHCP (Dynamic Host Configuration Protocol) automatically assigns an IP address, subnet mask, default gateway, and DNS server address to any device that newly joins a network β€” so nobody has to type those values in by hand.

  2. The Four-Step DORA Process

    When a device joins a network, it gets an IP address through four steps: Discover (the device broadcasts a request for an address), Offer (a DHCP server proposes a candidate address), Request (the device asks to use that specific address), and Acknowledge (the server confirms it).

  3. Lease Time

    An IP address handed out by DHCP is not owned permanently β€” it is "leased" for a set period. The device automatically requests a renewal before the lease expires, and if renewal fails, the address is returned to the pool and can be reassigned to another device.

  4. Scope and Address Pool

    Administrators define a scope β€” the range of IP addresses a DHCP server is allowed to hand out. Addresses outside that range are managed separately, for example as static IPs, so they never collide with automatically assigned ones.

  5. DHCP Reservation (Fixed Assignment)

    A reservation always hands out the same IP address to a specific device, identified by its MAC address. The device is still technically using DHCP, but in practice it ends up with a permanently fixed address, just like a static IP.

  6. DHCP Relay

    In networks split across multiple subnets, such as in a company, each subnet's router can relay DHCP requests to a central DHCP server. This means a separate DHCP server is not needed for every single subnet.

  7. DHCPv6 and IPv6 Environments

    In IPv6 environments, devices can configure their own addresses through SLAAC, use a DHCPv6 server that hands out addresses and DNS information, or use some combination of both depending on the setup.

If IP addresses keep conflicting

A tangled DHCP lease or a manually configured static IP can cause two devices to end up sharing the same address. Learning how to resolve an IP address conflict is worth doing if this happens more than once.

Want to set a fixed IP without relying on DHCP?

Some devices really do need the same address every time. Comparing DHCP reservation against manually configuring a static IP address on a PC is a good way to decide which approach fits your situation.

Frequently Asked Questions

Where does the DHCP server actually live?

At home, your internet router usually doubles as the DHCP server. In businesses or larger organizations, a dedicated DHCP server is more common.

Does my internet drop when the lease expires?

Usually not. Devices automatically request a renewal well before the lease period ends, so users rarely notice anything happening. Only in the rare case that renewal fails does a device have to go through the process of getting a new address.