DHCP (Dynamic Host Configuration Protocol) is the service that lets a device join a network without manually entering an IP address, subnet mask, gateway, and DNS server. On most home networks, the router runs the DHCP server.

What happens when a device joins?

The client asks for network configuration, a DHCP server offers an address and related options, the client requests the offer, and the server acknowledges the lease. The details are time-limited rather than permanent.

Why local IP addresses change?

A device may receive a different address when a lease expires, the router reboots, the DHCP pool changes, or the device uses randomized MAC addresses. That is normal for phones and laptops.

When to use a DHCP reservation?

Devices referenced by other settings—printers, NAS systems, local servers, port-forward targets—benefit from a stable address. A reservation tells the DHCP server to give the same address to a particular device while keeping central management.

Avoid pool conflicts

Do not manually assign an address inside the dynamic pool unless the router understands and reserves it. Two devices using the same IP can produce intermittent connectivity that is surprisingly hard to diagnose.

Lease lifecycle

A client discovers/offers/requests/acknowledges configuration in classic DHCPv4 behavior, then renews leases over time. The server can provide IP, mask, gateway, DNS and other options.

Reservations versus static addresses

A reservation keeps assignment centralized in DHCP. Manual static addresses are useful when required but should sit outside conflicting dynamic assignments and include correct gateway/DNS/prefix values.

Two DHCP servers

Accidental second routers/access points can answer the same LAN and give clients conflicting gateways/DNS, producing intermittent “internet” failures.

Video walkthrough for DHCP Explained: How Devices Get an IP Address, Gateway, and DNS Settings

Explains common DNS record types and how they fit together. DNS resolution is only one layer; a resolved hostname can still have a web, TLS or routing problem.