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Setting Custom DHCP Options

A DHCP option is a purposefully coded piece of data - either an IP address, string of text, or hex value. This data is used by DHCP clients when communicating with the network. The majority of network devices use the default options provided natively by many DHCP service providers, including the MX Security Appliance and MS Layer 3 Switch. However in some instances a DHCP deployment requires the configuration of additional DHCP options, most often when implementing DHCP with VoIP phones and other specific function devices.  

This article covers:

Configuring DHCP Options

  1. Navigate to Security appliance > Configure > DHCP (or, on the MS switch, Switch > Configure > Layer 3 > [the interface being edited] > DHCP settings)
  2. Select Add a DHCP option.
  3. Select the desired option from the list or if it isn’t listed, add a custom option.
  4. Input the DHCP code.
  5. Select the type as either IP or text.
  6. Enter the desired value for the option in the Value field.
  7. If the DHCP option calls for a hex value, set the type to “text” and enter the hex value as a text string using only hex characters.

 

 

Commonly used custom options

Many DHCP options can be specified on a DHCP server, though there are a few that tend to be used frequently. For more information on some of the more common DHCP options and what they configure, reference our article on Common DHCP Options.
Note: A full list of DHCP options and their definitions can be found here. Note that some DHCP option codes are reserved for vendor-specific options. Consult with vendor documentation to determine the code’s purpose for their devices.

Example DHCP option configurations

A connection-specific DNS domain suffix is assigned to DHCP clients using DHCP option 15. The steps below show how to assign DHCP option 15 in Dashboard.

  1. Navigate to Security appliance > Configure > DHCP (or, on the MS switch, Switch > Configure > Layer 3 > [the interface being edited] > DHCP settings)
  2. Find the setting DHCP options.
  3. Click Add a DHCP option.
  4. Choose Custom from the Option drop down.
  5. For Code enter 15, choose Text for Type, and for Value enter the DNS domain suffix.
  6. Click Save changes.

In this example meraki.com will assigned using DHCP Option 15.

 

An ipconfig /all from a Windows client shows the suffixes have been assigned:


 

In our second example, DHCP option 130 will direct Mitel Phones to be look back to the in-house Mitel Server to obtain DHCP information.

 

  1. Navigate to Security appliance > Configure > DHCP (or, on the MS switch, Switch > Configure > Layer 3 > [the interface being edited] > DHCP settings)
  2. Under DHCP options, click Add a DHCP option.
  3. Select Custom under the Option column.
  4. Under Code enter 130.
  5. Under Type enter Text.
  6. Under Value enter MITEL IP PHONE.

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Last modified
17:03, 18 Feb 2016

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ID: 1420

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