Lync Server 2013, like any unified communications product, depends
heavily on the network it is installed on to deliver needed
functionality. Whereas some network dependencies are obvious, such as
connectivity and sufficient bandwidth, other dependencies might not be
so evident, such as DHCP requirements, network site definitions, and
configuration of specific features on network switches.
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.
Note
Additional DHCP options might also be
required for Lync depending on the network. For example, the preferred
method of configuring phone devices with a dedicated voice VLAN is Link
Layer Discovery Protocol-Media Endpoint Discovery (LLDP-MED), but not
all Ethernet switches support this feature. Where LLDP-MED is not
supported, additional DHCP vendor classes and associated options can
instead be configured to supply the voice VLAN ID to the device.
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.
Note
Each Lync Front End Server also includes a
built-in DHCP component, which is disabled by default. The built-in
Lync DHCP service cannot provide IP address leases, and is simply used
to provide the values for DHCP options 43 and 120 for very small Lync
environments where IP addressing is handled manually.
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 Files\Common Files\Microsoft 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 Setup\amd64 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.
Tip
Only a 64-bit version of DHCPUtil.exe
is supplied with Lync Server 2013, and this cannot be used to configure
a 32-bit DHCP server. In this situation, the next best option is to run
DHCPUtil.exe directly on the Lync Front End Server, and
then use the output from the command to manually supply the values that
will be used with the DHCPConfigScript.bat script on the DHCP server.
