ichdasich / dhcp-client

Reference DHCP client in go

Golang DHCP Client Demonstration

A toy golang DHCP client to explore the DHCP protocol. Randomizes request MAC address as to not step on the same lease over and over.

Usage

./compile.sh
./toydhcp [-ip4 address]

Outline

• DHCP Protocol Diagram
• DHCP Packet Sequence
  1. DISCOVER
  2. OFFER
  3. REQUEST
  4. (N)ACKNOWLEDGE
• DHCP Option Codes
• Additional Reading

DHCP Protocol Diagram

Wikipedia - Gelmo96 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

DHCP Packet Sequence

DISCOVER

OFFER

REQUEST

(N)ACKNOWLEDGE

DHCP Option Codes

A small selection of important DHCP Option Codes

• 53 - DHCP Message Type (1B) - Indicates the specific type of DHCP message: DISCOVER(1), OFFER(2), REQUEST(3), DECLINE(4), ACK(5), NACK(6), RELEASE(7), INFORM(8)
• 50 - Requested IP Address (4B)
• 54 - DHCP Server Address (4B)
• 51 - Lease Time in Seconds (4B)
• 3 - Router IP Address (4B)
• 1 - Network Subnet Mask (4B)
• 255 - End Mark (1B)

Additional Reading

Wikipedia.org - DHCP
The TCP/IP Guide - DHCP Options