- Overview
- Dynamic Host Configuration Protocol version 4 (DHCPv4) allows for the automatic configuration of client systems on an Internet Protocol version 4 (IPv4) network. DHCPv4 eliminates the need to individually configure devices, allowing them to set network properties by connecting to the DHCPv4 server instead.
- Function
- Prerequisites :
- DHCPv4 server system
- DHCPv4 client system
- Navigable network connection between DHCPv4 server and DHCPv4 client When a new system is brought online (generally at boot) and needs to configure itself for communicating on the network it makes a broadcast looking for a DHCPv4 server. When the DHCPv4 server observes this broadcast it responds to the request with an offer that contains the information necessary to join the network. At its most basic level, this includes an IP address, netmask, the DHCP server's IP address, the default route/gateway, DNS server address(es), and the lease time (how long the offer will be good for). The DHCPv4 client then responds requesting the configuration offered. Finally, the DHCPv4 server responds acknowledging and granting the request. In shorter form, this transaction is as follows:
- Client requests information (the DHCPDISCOVER)
- One or more servers respond (the DHCPOFFER)
- Client selects one response and requests that configuration from the offering server (the DHCPREQUEST)
- The server which made the offer responds acknowledging the configuration (the DHCPACKNOWLEDGEMENT)
Example container DHCPDISCOVER:
| Bit Range | Bit Use Nominal | Value |
| 0 - 15 | Source Port Number | 01000011 |
| 16 - 31 | Destination Port Number | 01000100 |
| 32 - 47 | Packet Length | 0000000101001000 |
| 48 - 63 | Checksum | varies |
| 64 - 71 | Operation Code (OP) | 00000001 |
| 72 - 79 | Hardware Address Type (HTYPE) | 00000001 |
| 80 - 87 | Hardware Address Length (HLEN) | 00000110 |
| 88 - 95 | Hops (HOPS) | 00000000 |
| 96 - 127 | Transaction ID (XID) | varies |
| 128 - 143 | Seconds Since Client Started Request (SECS) | 0000000000000000 |
| 144 - 159 | Flags (FLAGS) | 0000000000000000 |
| 160 - 181 | Client IP Address (CIADDR) | 00000000000000000000000000000000 |
| 182 - 213 | Your IP Address (YIADDR) | 00000000000000000000000000000000 |
| 214 - 245 | Server IP Address (SIADDR) | 00000000000000000000000000000000 |
| 246 - 277 | Relay IP Address (GIADDR) | 00000000000000000000000000000000 |
DHCPOFFER
| Bit Range | Bit Use |
| a - b | Use |
DHCPREQUEST
| Bit Range | Bit Use |
| a - b | Use |
DHCPACKNOWLEDGEMENT
| Bit Range | Bit Use |
| a - b | Use |
1.8.17