Description

This article explains how to configure Dynamic Host Configuration Protocol (DHCP) option 150 and DHCP option 66 for EX Switches.

DHCP Option 150 is a Cisco proprietary DHCP setting. The IEEE standard that matches with this setting is Option 66. Like Option 150, Option 66 is used to specify the name of the Trivial File Transfer Protocol (TFTP) server.

Symptoms

What is the difference between DHCP Option 150 and DHCP Option 66?

Solution

For Cisco phones, IP addresses can be assigned manually or by using Dynamic Host Configuration Protocol (DHCP). Devices also require access to a Trivial File Transfer Protocol (TFTP) server, which contains the device configuration name files (.cnf file format) and enables the device to communicate with Cisco Call Manager.

Cisco IP Phones download their configuration from a TFTP server. When a Cisco IP Phone starts, if it does not have both the IP address and the TFTP server IP address pre-configured, it sends a request with DHCP Option 150 to the DHCP server to obtain this information.

DHCP Option 150 is a Cisco proprietary setting. The IEEE standard, which matches this requirement, is DHCP Option 66. Like Option 150, Option 66 is used to specify the name of the TFTP server. Option 66 is an Open Standard configuration option and Juniper supports it. RFC 2132 defines Option 66.

Difference between Option 150 and Option 66

  • DHCP Option 150 supports a list of TFTP servers (multiple server IP addresses).

  • DHCP Option 66 supports the IP address or the hostname of only a single TFTP server.

The following configuration can be used to achieve the required configuration:  

set system services dhcp pool 10.1.1.0/24 boot-file test.cnf      // option 67 
set system services dhcp pool 10.1.1.0/24 next-server 20.1.1.25  // option 66
We can specify the next server (TFTP server) both globally or specific to a pool. If the next server is configured in both places, then the IP address specified under the pool will be used. 

Note: Ensure that you reference the "option" function, which is available under the [edit system services dhcp] stanza. The dhcp option along with byte-stream allows further option flexibility. 

Modification History

2026-02-09: Minor-non-technical changes made for search optimization