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DHCP Address Assignment

Summary: DHCP is how a router automatically gives a joining device a private IP address. The address is leased for a set time, renewed while the device stays connected, and recycled when the lease expires.

At a glance​

QuestionAnswer
What is it?Automatic assignment of IP addresses to devices joining a network
Why does it matter?No manual network setup; addresses are reused instead of exhausted
When do I use it?Understanding why a device got, kept, or changed its local IP

How it works​

  • A device joins and asks for an address. The router picks a free one from its pool and leases it. The exchange is often summarized as DORA: Discover, Offer, Request, Acknowledge.
  • A lease lasts a set time, for example 24 hours. The device renews it in the background while connected.
  • If the device leaves and doesn't renew, the lease expires and the address returns to the pool.
  • The router recognizes returning devices by MAC address, so it often hands back the same IP.

Why the table stays small​

  • The pool is bounded. A typical home network has about 250 usable addresses.
  • Expired entries are overwritten as devices come and go rather than stored forever, so the router needs very little memory for this.

MAC address caveat​

  • A MAC address is a hardware ID assigned at the factory, but it can be changed in software.
  • Modern phones and laptops often use a randomized "private" MAC per Wi-Fi network. The router may then treat a familiar device as new, and it may get a different IP.

Remember​

  • A DHCP address is borrowed, not owned.
  • Same MAC usually means same IP; a randomized MAC can break that.