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VDI planning primer on DHCP scope options

Fellow virtualization expert Andrew Kutz has argued that future virtual desktop infrastructure technologies (VDI) need to lose the desktop to truly advance VDI technology, and I agree. But until that time, we have to deal with VDI as it exists today. And that means accepting certain hurdles, which means accepting additional support requirements that today’s VDI poses. Let’s consider devices and their support requirements.The key to determining how virtual desktop infrastructure (VDI) devices interact with their connection broker is to identify the networking configuration. VDI devices use dynamic host control protocol (DHCP) scope options to get their configurations to the device that reflects where they go for the connection. Let’s dive into how the DHCP options are important to a VDI solution.

For starters, a DHCP scope option is a configuration that is defined on a networking server such as Windows Server’s DHCP server role. Traditional configurations for PCs and servers would have DHCP options such as subnet mask, default gateway and domain name server. VDI, however, allows the full range of DHCP scope options to be used. There are numerous scope options available for DHCP that are delivered to the requesting device in the acknowledgment message (DHCPACK), which is sent after the DHCP request message.

DHCP scope options vary by VDI device. Take for example the SunRay series of VDI devices. For VDI solutions in VMware implementations, the technology requires that at least DHCP options 49 and 66 are configured for connection to the Virtual Desktop Connector agent. Option 49 is for an X11 server window manager and 66 is a trivial file transfer protocol (TFTP) server for VDI device configuration files.

Beyond basic configuration, it may be worth tweaking some other network options based on the architecture of the VDI implementation. What has particularly caught my attention is a blog post by Sun’s Thin Client and Server Based Computing group, which points out that some environments may need to configure the maximum transmission unit (MTU) of network packets. This can also be assigned by DHCP and is of particular importance if the VDI implementation is to be a remote site with limited bandwidth. The default MTU of most configurations is around 1,500 bytes, yet performance may be better with a smaller number for maximum packet size from the endpoint VDI device. This and other factors make a fully representative pilot sound like a really good idea!

However, other platforms may use a new set of options to interact differently with the VDI device firmware. One example is the Pano Logic desktop device, which only requires the creation and configuration of option 001 as a vendor class. This is different than the example above in that there is no X11 window manager resident on the device.

While these DHCP configuration options are not overwhelming when viewed individually, it is worth considering the larger picture in the case of these options already in use. The most common example is an IP telephone at a remote site. While in central offices, IP telephony is usually split to a separate network, but this may not be the case for remote sites that have two or three VDI stations and the same number of phones. It may make sense to have only one IP network.

DHCP is critical to effective network management, including a VDI solution. Some planning on scope and configuration can go a long way to ensure that the technology will function as expected.