DHCP Various Server options

Common Options

Here is the list of the most common DHCP options exchanged with clients:

DHCP option 1: subnet mask to be applied on the interface asking for an IP address

DHCP option 3: default router or last resort gateway for this interface

DHCP option 6: which DNS (Domain Name Server) to include in the IP configuration for name resolution

DHCP option 51: lease time for this IP address

Interesting Options

Below is the list of other interesting options that can be provided to clients to ease their initial configuration:

DHCP option 2: time offset in seconds from UTC to be applied on the current time (note: deprecated by RFC4833 – options 100 and 101)

DHCP option 4: list of time server as stated in the RFC868 (Time Protocol)

DHCP option 12: host name of the client, very useful for IoT and any device without user

DHCP option 15: specifies the domain name that client should use as suffix when resolving hostnames via the Domain Name System

DHCP option 42: list of the NTP Servers by order of preference, used for time synchronization of the client

DHCP option 58 and 59: Renewal Time Value (T1) and Rebinding Time Value (T2). See the chapter “DHCP Lease Time Management” on What is DHCP?

DHCP options 69 and 70: respectively for SMTP and POP3 servers for sending and receiving email. We do see these options often on printers and scanners

DHCP option 81: Client Fully Qualified Domain Name – this option allows to perform automatic update of the DNS records associated to the client, mainly the A and PTR. In the option we can specify whether the client or the server will update the records and the FQDN associated to the client. It is defined in the RFC4702

DHCP option 100: time zone POSIX string as in IEEE 1003.1

DHCP option 101: time zone as a string like in the TZ database (eg: Europe/Paris)

DHCP option 119: DNS domain search list that will be used to perform DNS requests based on short name using the suffixes provided in this list.

DHCP option 121: classless static route table composed of multiple network and subnet mask, this option replaces the original one numbered 33 (see RFC3442)

references:

https://www.efficientip.com/glossary/dhcp-option/