Connectivity Guide

Figure 2. Client and Server Messaging
DHCP server Network device offering configuration parameters to the client.
DHCP client Network device requesting configuration parameters from the server.
Relay agent Intermediary network device that passes DHCP messages between the client and the server when the
server is not on the same subnet as the host.
Packet format and options
The DHCP server listens on port 67 and transmits to port 68. The DHCP client listens on port 68 and transmits to port 67.
Configuration parameters are options in the DHCP packet in type, length, value (TLV) format. To limit the number of parameters
that servers must provide, hosts enter the parameters that they require and the server sends only those parameters. DHCP
uses the User Datagram Protocol (UDP) as its transport protocol.
Figure 3. DHCP Packet Format
The table shows common options using DHCP packet formats.
DHCP Option
Description
Subnet mask 1 — Subnet mask of the client
Router 3 — Router IP addresses that serve as the default gateway for the client
Domain name
server
6 — Domain name servers (DNS) that are available to the client
Domain name 15 — Domain name that clients use to resolve hostnames via DNS
IP address lease
time
51 — Amount of time that the client uses an assigned IP address
DHCP message
type
53:
● 1 — DHCPDISCOVER
● 2 — DHCPOFFER
● 3 — DHCPREQUEST
● 4 — DHCPDECLINE
● 5 — DHCPACK
● 6 — DHCPNACK
● 7 — DHCPRELEASE
System management 123