Let’s assume you are in a hotel and you want a room to sleep in. Of course you can’t just pick a random room and take it — you need the receptionist Alice, who will help you with the DORA process. That means: you (D)iscover by asking “does anyone have a room for me?”, and Alice will notice and (O)ffer you one. You tell her how long you want to stay and (R)equest it — yes, you want that room for 3 days. She gives you the keys and (A)cknowledges that you took the room.
That’s the heart of DHCP (Dynamic Host Configuration Protocol). But instead of a physical room, it lends you a digital address: an IP. If it didn’t exist, every time you added a device to your network you’d have to look up which IP is free and register it by hand. Sometimes a static IP is important — for example for your router — but most of the time DHCP makes your day easier.
Checkout is at eleven
To not run out of IPs, DHCP also gives every address a lease time, which depends on the type of network. In a public network at an airport, hundreds of people each day need a temporary IP, so the lease time is likely 1 to 8 hours. In your home network, your devices might lease an IP for up to 30 days.
The evil receptionist
Just like ARP, DHCP was designed with a lot of trust: your device takes the first offer it gets. If an attacker runs a rogue DHCP server in your network and answers faster than the real one, he can hand out his own machine as your gateway and DNS server — and suddenly all your traffic makes a detour through him. Combine that with DHCP starvation (requesting leases until the real server runs out of rooms) and the fake front desk is the only one left answering.