# Q5(c) · DHCP dynamic allocation

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2024-feb-reexam/q5c

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/papers/paper-2024-feb-reexam--q5c/

Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.

### Q5(c). Explain the working of DHCP protocol highlighting dynamic IP address allocation. [5 marks]

### Answer

**Definition.** Dynamic Host Configuration Protocol (DHCP) provides IP configuration parameters to clients and can lease reusable addresses for limited periods.

**Simple meaning.** DORA = Discover, Offer, Request, Acknowledge.

Swipe across the diagram to read its labels ↔

![DHCP initial allocation: DORA](https://deep-learning-study-room.vercel.app/cn/fig/dhcp.510e8eca42.svg)

Diagram: DHCP initial allocation: DORA. Labels: DHCP initial allocation: DORA | DHCP initial allocation: DORA | Client | Server | DISCOVER | OFFER | REQUEST | ACK | Client asks → server offers → client chooses → server confirms.

DHCP: automatic configuration through DORA

## Understand it step by step

1. **Discover:** a new client looks for DHCP servers. With no configured IPv4 address, it commonly starts from 0.0.0.0 and uses broadcast discovery.
2. **Offer:** a server offers an address and configuration, such as subnet mask, lease information and other options.
3. **Request:** the client indicates the selected offer and requested address. In initial allocation this also informs other servers of its choice.
4. **Acknowledge:** the selected server confirms the lease/configuration. The client can then use the address after the required checks.
5. DHCPv4 uses UDP server port 67 and client port 68. A DHCP relay can carry requests between a client subnet and a server elsewhere; ordinary routers do not simply forward local broadcasts by default.

#### Practical example

When a laptop joins a campus network, DHCP can supply its address, mask, gateway and DNS-server option. It does not itself resolve website names; it can tell the laptop which DNS server to use.

1. DHCPDISCOVER: client searches for a server.
2. DHCPOFFER: server proposes an address/configuration.
3. DHCPREQUEST: client requests the chosen allocation.
4. DHCPACK: server confirms the lease.

DHCP reduces manual configuration and supports controlled address reuse through leases.

**Yaad rakho:** Discover–Offer–Request–ACK; pehle D, phir O, phir R, phir A.