---
title: "Short note: DHCP"
subject: "Internet and Intranet"
chapter: 3
key: "semester_8/internet_and_intranet:note-dhcp"
source: https://www.bctengineer.com/q/semester_8/internet_and_intranet/note-dhcp
site: BCT Engineering
---

# Short note: DHCP

Internet and Intranet · Chapter 3: Protocols and Client/Server Applications

- Asked in: 2072 Magh, 4 marks
- Video: [DHCP Explained - Dynamic Host Configuration Protocol](https://www.youtube.com/watch?v=e6-TaH5bkjo) — PowerCert Animated Videos
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/internet_and_intranet/note-dhcp
- Whole chapter: https://www.bctengineer.com/md/semester_8/internet_and_intranet/chapter-3

## Question

Write a short note on DHCP.

## Short answer

DHCP automatically assigns IP addresses and network settings using DORA (Discover, Offer, Request, Ack) over UDP ports 67 and 68. It supports dynamic, automatic, and manual allocation with lease renewal.

## Answer

**Dynamic Host Configuration Protocol (DHCP)** is an application layer protocol (RFC 2131) that automatically gives a host its network configuration: IP address, subnet mask, default gateway, DNS server addresses and lease time. It removes manual configuration and reduces address conflicts. It is a client/server protocol using UDP: server port **67**, client port **68**.

**Four-step process (DORA)**

1. **DHCP Discover**: the new client broadcasts to 255.255.255.255 looking for a server.
2. **DHCP Offer**: the server offers an unused IP address, mask, lease time (broadcast or unicast).
3. **DHCP Request**: the client broadcasts the chosen offer (so other servers know).
4. **DHCP Ack**: the server confirms and the client starts using the address.

```text
 Client                         DHCP Server
   |---- Discover (broadcast) ----->|
   |<------- Offer -----------------|
   |---- Request ------------------>|
   |<------- Ack -------------------|
```

**Features**

- Address allocation: **dynamic** (leased from a pool), **automatic** (permanent) and **manual** (fixed by MAC address, reservation).
- Leases are renewed at 50% (T1) of the lease time; the address returns to the pool when released or expired.
- A **DHCP relay agent** forwards requests across routers so one server can serve many subnets.
- Useful in intranets, Wi-Fi, ISPs and laptops that move between networks.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the order of the DHCP process?
   A. Offer, Discover, Ack, Request
   B. Discover, Offer, Request, Ack
   C. Request, Discover, Offer, Ack
   D. Discover, Request, Offer, Ack
   Answer: B. The client broadcasts Discover, the server sends Offer, the client broadcasts Request, and the server confirms with Ack. (Key point: DORA sequence)

2. Besides an IP address, what does DHCP typically supply?
   A. Only a MAC address
   B. Subnet mask, default gateway, DNS servers and lease time
   C. A domain registration
   D. A TLS certificate
   Answer: B. DHCP automatically configures IP address, mask, gateway, DNS server addresses and lease time. (Key point: What DHCP provides)

3. What is the purpose of a DHCP relay agent?
   A. To forward client requests across routers so one server can serve many subnets
   B. To encrypt DHCP messages
   C. To assign static addresses only
   D. To replace the lease mechanism
   Answer: A. Broadcasts do not cross routers, so a relay agent forwards them to a central DHCP server. (Key point: Relay agent)