What is DHCP and what is the DORA process?
DHCP auto-assigns IP addresses and other settings via the four-step DORA exchange: Discover, Offer, Request, Acknowledge.
DHCP (Dynamic Host Configuration Protocol):
A service that automates the assignment of IP addresses, subnet masks, gateways, and other IPv4 networking parameters.
* DORA: Discover, Offer, Request, Acknowledge — the four-step lease handshake. *
Static vs Dynamic Addressing:
- Static: Manually configured, used for servers, printers, network devices
- Dynamic (DHCP): Automatically assigned from a pool, used for end-user devices
The DORA Process (4 messages):
| Step | Message | Direction | Type |
|---|---|---|---|
| 1 | DHCPDISCOVER | Client → Server | Broadcast |
| 2 | OFFER | Server → Client | Unicast |
| 3 | REQUEST | Client → Server | Broadcast |
| 4 | ACK | Server → Client | Unicast |
Process Details:
- DISCOVER: Client broadcasts to find available DHCP servers
- OFFER: Server offers a lease with IP configuration
- REQUEST: Client formally requests the offered address (broadcast so other servers know)
- ACK: Server acknowledges and finalizes the lease
Lease Renewal: If lease is no longer valid, the server responds with DHCPNAK (negative acknowledgment) and client must restart with DHCPDISCOVER.
Note: The DHCPv6 messages that mirror this stateful DORA exchange are SOLICIT, ADVERTISE, REQUEST, and REPLY. (A separate two-message INFORMATION-REQUEST / REPLY exchange is the stateless DHCPv6 mode, used to fetch options like DNS without leasing an address.)
Go deeper:
-
DHCP Explained — Dynamic Host Configuration Protocol — PowerCert's animated DORA walkthrough. -
RFC 2131 — Dynamic Host Configuration Protocol — the DHCP standard and the four message phases. -
DHCP (Wikipedia) — DORA, lease renewal, and the DHCPv6 variant.