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Configuring Custom DHCP Options (NSM Procedure)

 

When configuring a DHCP server, you can also configure custom DHCP options to handle address assignment for voice-over-IP (VoIP) phones.

Note

Custom DHCP options are not supported on the NetScreen-500, the NetScreen-5200, the NetScreen-5400, the ISG1000 and the ISG2000.

A custom DHCP option contains:

  • Option Name—A user-defined, unique name that identifies the custom option.

  • Code—An arbitrary integer that represents the option type. Use the option code to represent the custom option you want to configure. For each DHCP server, you can configure an unlimited number of custom DHCP options; however, the option code for each custom option must be unique, and cannot match the option code for a predefined option (DHCP contains several predefined option codes). Table 1 lists the predefined option codes and associated RFC 2132 terms:

    Table 1: DHCP Option Codes

    Netmask

    1

    Gateway

    3

    DNS1, DNS2, DNS3

    6

    Domain Name

    15

    WINS1, WINS2

    44

    Lease

    51

    SMTP

    69

    POP3

    70

    News

    71

    NIS1, NIS2

    112

    NISTAG

    113

    In addition to predefined option codes, the codes 0, 255, and 53 cannot be used to create a custom DHCP option. All other integers between 2 and 254 are valid.

  • Data Type—The type of data required for the option code. Available data types are string, IP address, and integer.

  • Value—The value of the option code. When the data type is string, the acceptable length is 1-128 characters.

Your network recently added support for VoIP, and you now need to support DHCP for VoIP phones. You edit the existing DHCP server configuration to send the following custom options to IP phones acting as DHCP clients:

  • Option code 444, containing string “Server 4”

  • Option code 66, containing IP address 1.1.1.1

  • Option code 160, containing integer 2004

The example assumes that you have already configured a security device to act as a DHCP server.

To customize your DHCP options:

  1. In the NSM navigation tree, select Device Manager > Devices. Double-click the device currently handling your DHCP assignments.

  2. In the device navigation tree, select Network > Interface. Double-click an interface. The General Properties screen appears.

  3. In the interface navigation tree, select DHCP, set the DHCP mode to Server, and then select the Custom Options tab.

  4. Click the Add icon to add the first custom option. Configure the following options, and then click OK:

    • For Option Name, enter IP Address.

    • For Code, enter 66.

    • For Data Type, select IP ADDR.

    • For Value, enter 1.1.1.1.

    • Click the Add icon to add the second custom option. Configure the options as mentioned in Step 4, and then click OK:

  5. Click OK to save your changes to the interface, and then click OK again to save your changes to the device.