Lecture Notes: Understanding DHCP in Modern Networks

Introduction

• Modern networks allow easy communication without manual configuration.
• Previously, IPv4 configurations were manual: IP address, subnet mask, DNS settings.
• BootP Protocol: Early protocol to automate IP configuration.
  • Limitations: Did not recognize when IP addresses became available.

DHCP Overview

• DHCP (Dynamic Host Configuration Protocol): Automatically configures network devices.
• Successor to BootP with improved functionalities.

DHCP Process: DORA Steps

1. Discover

   • Device sends a DHCP discover packet to identify DHCP servers on the network.
   • Sent from IP address 0.0.0.0 as a broadcast to 255.255.255.255.
   • Uses UDP port 68 to port 67.

2. Offer

   • DHCP server offers an IP address to the device.
   • Sent as a broadcast from server’s IP (e.g., 10.10.0.99) to UDP port 68.

3. Request

   • Device requests the offered IP address from the server.
   • Packet structure similar to Discover, sent to all devices.

4. Acknowledgement

   • DHCP server confirms the IP address assignment to the device.
   • Sam's device configures IP settings based on the server's information.

Network Diagram Example

• Sam's Process
  • Sam connects the laptop, needs an IP address.
  • Single DHCP server on the network.
  • Router connects to another network switch and remote workstation (Jack).

DHCP Limitations & Solutions

• Broadcast Limitation: Broadcasts limited to local subnet, do not traverse routers.

  • Challenge: Difficulties in having redundant and distributed DHCP servers.

• DHCP Relay (Helper)

  • Centralizes DHCP servers, avoids spreading servers across remote sites.
  • Routers configured with DHCP relay allow DHCP traffic across subnets.
  • Converts broadcast requests to unicast communications.
  • Example: Jack’s workstation gets IP via a relay.

Conclusion

• DHCP enhances network scalability by automating IP configuration.
• Relay features address challenges of broadcast limitations, enabling efficient IP address assignment across diverse network architectures.