# IPv4 - DHCP

[TOC]

## 課程影片

### Introduction to DHCP (with demos in Linux)

{%youtube SL56sVAzxSE %}

### 第 7LMN 講 路由器運作原理以及網路互連技術 L07 12 13 14

{%youtube 4aRXm4ujh7g %}

### Lec36 計算機網路 第四章 Internet Protocol Layer (10/19)

{%youtube XrpQl7gtAlg %}

## 目標：動態地分配 IP 位址

現在已經有分配一個網段的 IP 了，問題就是哪台機器要拿哪個 IP？

## DHCP 封包格式

取自 [RFC2131](https://datatracker.ietf.org/doc/html/rfc2131)：

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     op (1)    |   htype (1)   |   hlen (1)    |   hops (1)    |
   +---------------+---------------+---------------+---------------+
   |                            xid (4)                            |
   +-------------------------------+-------------------------------+
   |           secs (2)            |           flags (2)           |
   +-------------------------------+-------------------------------+
   |                          ciaddr  (4)                          |
   +---------------------------------------------------------------+
   |                          yiaddr  (4)                          |
   +---------------------------------------------------------------+
   |                          siaddr  (4)                          |
   +---------------------------------------------------------------+
   |                          giaddr  (4)                          |
   +---------------------------------------------------------------+
   |                                                               |
   |                          chaddr  (16)                         |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+
   |                                                               |
   |                          sname   (64)                         |
   +---------------------------------------------------------------+
   |                                                               |
   |                          file    (128)                        |
   +---------------------------------------------------------------+
   |                                                               |
   |                          options (variable)                   |
   +---------------------------------------------------------------+