Supporting Lync Phone Edition with DHCP

Whereas Lync software clients inherit network connectivity from the host they are installed on, networking for specialized devices such as VoIP desk phones is typically managed centrally. Traditionally, these devices are configured via dynamic host configuration protocol (DHCP), not only for IP addressing assignments but also as a centralized method of informing the devices that updated firmware is available. To allow centralized management of Lync Phone Edition devices, specific DHCP requirements must be met.

Standard enterprise DHCP services, such as the DHCP server role integrated with Windows Server operating systems, can be used to meet Lync DHCP requirements. However, there are unique DHCP options that are used to support Lync Phone Edition devices, including the following:

• Option 43—A specialized DHCP option that consists of a series of sub-options. With Lync Server, these sub-options are used to specify the Lync Pool Certificate Provisioning Service URL in the form of https://WebPoolDFQDN:443/CertProv/CertProvisioningService.svc.

• Option 120—Specifies the list of SIP servers that can handle authentication requests for the device.

• Option 55—Supplies the values of DHCP options 43 and 120 to the DHCP client.

• Option 60—Specifies the vendor for which option 43 provides sub-options.

• Option 4—Specifies an NTP server to ensure that time on the device remains in sync with other systems on the network.

Although several of the DHCP options previously listed are very straightforward for anyone familiar with DHCP, option 43 in particular can be challenging to configure correctly, due to the fact that numerous sub-options are used, each involving hex-encoded binary strings. Thankfully, Microsoft provides the DHCPUtil utility along with an associated script, which together can be used to generate and then apply the correct values for options 43 and 120 to a Microsoft DHCP server. For environments where a non-Microsoft DHCP server is used, these values will need to be configured manually in order to support Lync Phone Edition devices.

The following procedure is used to configure DHCP options 43 and 120 using DHCPUtil:

1. Copy the DHCPUtil.exe and DHCPConfigScript.bat files from the following location on a Lync Front End Server to a local subdirectory on the DHCP server: C:Program FilesCommon FilesMicrosoft Lync Server 2013.

2. If it is not already installed, install the Microsoft Visual C++ Redistributable Package on the DHCP server as a prerequisite for running DHCPUtil.exe (located in the Setupamd64 directory on the Lync media with a filename of vcredist_x64).

3. On the DHCP server, open an elevated command prompt. Navigate to the subdirectory where the files were copied previously in step 1, and execute the following command, in which the fully qualified name of the Lync pool is used as <PoolName>: DHCPUtil.exe -SipServer <PoolName> -RunConfigScript. A series of netsh commands executes, configuring the appropriate values for DHCP options 43 and 120 within the local DHCP instance.