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DHCP option 150 and DHCP option 66

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Article ID: KB16352 KB Last Updated: 02 Jul 2013Version: 2.0
Summary:
This article provides an understanding for configuring option 150 and to use option 66 for EX Switches.DHCP Option 150 is Cisco proprietary. Option 66 is an IEEE standard.
Symptoms:

Solution:
For Cisco phones IP addresses can be assigned manually or by using DHCP. Devices also require access to a TFTP server that contains device configuration name files (.cnf file format), which 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 TFTP server IP address pre configured, it sends a request with option 150 to the DHCP server to obtain this information.

DHCP Option 150 is Cisco proprietary. The IEEE standard that matches with this requirement is Option 66. Like option 150, option 66 is used to specify the Name of the TFTP server.

Option 66 is an open standard 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 IPs)

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

The following configuration can be used to achieve this requirement:

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 specified under the pool will be used.

NOTE: Please also reference the "option" function available under the {edit system services dhcp] stanza.  The dhcp option along with byte-stream allows further option flexibility.  The "byte-stream" option is available in JUNOS software release 9.5R3 and higher.


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