Obtaining Values of DHCP Options by Using DHCPUtil.exe


Topic Last Modified: 2012-06-21

You can use the DHCPUtil.exe tool to configure DHCP options on a Windows DHCP server. (If you plan to use other DHCP servers in your deployment, check the DHCP server documentation about how to configure the options.) The following section describes the DHCP options that you’ll configure and how you can use DHCPUtil.exe to obtain the byte values that are required to set the DHCP option values.

DHCP Option 120

Important details about DHCP option 120 include:

  • The encoding type is 0.

  • Following the encoding type, the general pattern is the length of a portion of the fully qualified domain name (FQDN) followed by ASCII codes for the corresponding characters (for example, 97 for “a”).

  • Each character is actually 1 byte with a value that is equal to the ASCII code for the respective character.


    You can use DHCPUtil.exe to obtain the value for DHCP option 120. Note that DHCPUtil supports specifying no more than one Lync Server Front End pool FQDN.

For details about DHCP option 120, see RFC 3361.

DHCP Option 43

Lync Server and the IP phone clients use DHCP option 43 by including a new vendor class identifier. This is specified as DHCP option 60 (for details, see RFC 2132, Section 9.13). To discover Lync Server Windows Certificate Services, the IP phones set DHCP option 60, which is the vendor class identifier, to MS-UC-Client (case-sensitive).

The IP phone makes two DHCP option 43 requests: a VLAN ID request (vendor class ID: CPE-OCPHONE) and a certificate provisioning service URL request (vendor class ID: MS-UC-Client). The certificate provisioning service URL request is made up of the following vendor-specific sub-options. For devices to discover the Lync Server Certificate Provisioning service, these sub-options must be configured:


You can use DHCPUtil.exe to obtain the value for these sub-options. See the next section for details.

  • Id= 1, value =4D532D55432D436C69656E74, description = MS-UC-Client

  • Id=2, value=6874747073<Can vary with deployment, but generally is constant >, description=URL Scheme

  • Id=3, value=<varies with deployment>, description=Lync Server Internal Web FQDN

  • Id=4, value=343433 (Can vary with deployment, but generally is constant), description=Lync Server Web Server Port

  • Id=5,value=< /CertProv/CertProvisioningService.svc - 2F4365727450726F762F4365727450726F766973696F6E696E67536572766963652E737663>, description=Relative Path to the Lync Server Certificate Provisioning service

Using DHCPUtil.exe to obtain DHCP Option 120 and 43 values

To use DHCPUtil.exe to obtain the value for various sub-options for option 43, do the following:

  1. Install Microsoft Visual C++ 2008 Redistributable Package (x86) to run DHCPUtil.exe for DHCP options.

  2. At a command prompt, run:

    DHCPUtil.exe -SipServer <Lync Server Pool FQDN > -WebServer <Lync Server Internal Web FQDN> -RunConfigScript

The Lync Server internal web FQDN is the FQDN of the web components that run on the Lync Server Front End pool. This is typically specified by using Topology Builder as part of the pool properties. If you do not use Domain Name System (DNS) load balancing for the pool, the Lync Server internal web FQDN is the same as the Lync Server pool FQDN.

Use the values generated by DHCPUtil.exe to configure your DHCP server. For example:

Sip Server FQDN: ocspool1.contoso.com
Certificate Provisioning Service URL: https://ocspool1.contoso.com:443/CertProv/CertProvisioningService.svc

DHCP Option 120 Value:

DHCP Option 43 Value:
Vendor Class Identifier: MS-UC-Client
Option 43 (for vendor=MS-UC-Client):
               sub-option 1 <UC Identifier>: 4D532D55432D436C69656E74
               sub-option 2 <URL Scheme>: 6874747073
               sub-option 3 <Web Server FQDN>: 6F6373706F6F6C312E636F6E746F736F2E636F6D
               sub-option 4 <Port>: 343433
               sub-option 5 <Relative Path for Cert Prov>: 2F4365727450726F762F4365727450726F766973696F6E696E67536572766963652E73763