DHCP Option 150 & DHCP Option 66

Here we will provide 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.

PROBLEM OR GOAL:

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:

Juniper DHCP Option66 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 specified under the pool will be used.

Cisco DHCP Option150 Configuration:

ip dhcp pool vlan 10

network 192.168.10.0 255.255.255.0

default-router 192.168.10.254

option 150 ip 10.10.22.99 10.10.22.100(Configure 2 IP)

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.

 

More Experience of DHCP Configuration for Cisco VOIP Phones from users:

Option Code 150: DHCP Configuration for Cisco VOIP Phones

“I spent Saturday at the office finalizing some of the network functionality in our two offices.  One of the main things we needed to implement was a DHCP server at the satellite office, because our DHCP needs go beyond what the Cisco router we use can offer.  Primarily the limitation is in regards to requiring multiple domains in our search path for the DHCP clients.  In any case, we decided to simply install a Linux server (Debian 5.0 in this case) and run DHCP from there.

Installing and configuring DHCP is nothing new for me, and it was configured fairly quickly for the three subnets we use in that office.  The difficult part, and the part I had to spend some time on Google looking up, was in regards to our Cisco Phones.  Because we would be disabling the Cisco router DHCP functionality it all had to be replaced on the Linux server.  I had never needed to deal with DHCP in regards to Cisco phones before, but it is actually a fairly simple fix.  Here is an example:

authoritative;
ddns-update-style none;
option voip-tftp-server code 150 = ip-address;
option voip-tftp-server 192.168.134.192;

By adding the two “option” lines in my global configuration I was able to support the Cisco phones requirement for DHCP.  Note: I did try to put this within the subnet declaration for the phones specifically, but this is an option that cannot be nested.  In other words, it has to go in the global conf or it’ll complain and not start.

This should likely work for you as well, just make sure you replace the IP for “voip-tftp-server” with the address to your core phone server.  Hopefully the next time someone hits google looking for “option code 150 cisco phone” the clear answer isn’t so hard to find.”

More Related Networking and Configuration Tips:

Five Things You Should Know About DHCP Snooping

Cisco CCNP: How to Configure IP Source Guard?

How to Configure DHCP Snooping?

How to Configure DHCP Snooping in a Cisco Catalyst Switch?

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