IP address consumption doubles when you deploy virtual desktops, so it's important that IP address management is...
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When an organization begins working toward implementing VDI, it has a lot of things to consider: Is the storage connectivity fast enough? Do the host servers have enough memory? Will the end-user experience be acceptable?
These are all important questions, but one aspect of the preparation process that is sometimes overlooked is the affect that desktop virtualization will have on IP address consumption.
How virtualization consumes IP addresses
There are three primary ways that desktop virtualization affects IP address consumption. The first has to do with changes that you may need to make to your DHCP configuration.
Depending on how many virtual desktops you want to support, you may need to create additional DHCP scopes. You might even need to deploy some extra DHCP servers. This certainly isn't necessary in every situation, but it happens often enough to make it worth mentioning.
The second way IP address consumption becomes a factor is that the organization may suddenly consume far more IP addresses than it did prior to the desktop virtualization implementation. The reason for this is quite simple.
Consider an environment without virtual desktops. Each PC consumes an IP address, as do any backend servers. Shops implementing virtual desktops or VDI sometimes overlook the fact that desktop virtualization does not eliminate desktop hardware needs. Regardless of whether users connect via tablets, thin client devices or repurposed PCs, the endpoint consumes an IP address, and so does each virtual desktop.
This means that desktop virtualization effectively doubles IP address consumption on the client side. Each user consumes at least two IP addresses: The physical hardware uses one address and the virtual desktop uses another. There is no way to get around this requirement, so you must ensure that an adequate number of IP addresses are available to support virtual desktops and endpoints.
The third reason IP address consumption increases in a virtual desktop environment has to do with the way workers use virtual desktops. Employees can use virtual desktops on a wide variety of devices, such as PCs, smartphones and tablets. This gives workers the freedom to use the device that makes the most sense in a given situation. But IP address consumption does not mirror device use in real time.
When a device connects to the network, a DHCP server issues the device an IP address lease, but the lease isn't revoked when the device disconnects from the network. The lease remains in effect for a predetermined length of time, regardless of whether the device is still being used. As such, the IP address is only available to the device that leased it; it's not available for other devices to access during the lease period.
Desktop virtualization by its very nature leads to increased IP address consumption. The actual degree to which the IP addresses are consumed varies depending on device usage, however. From a desktop standpoint, you can expect the IP address consumption to double, but in organizations where workers use multiple devices, consumption can be even higher.
How to protect the network against increased IP consumption
The first thing I recommend doing is implementing session limits. Remember, every virtual desktop that is powered up consumes an IP address. You can establish some degree of control over the IP address consumption by limiting the number of concurrent sessions that users are allowed to establish. If each user is only allowed to have one or two concurrent sessions, then you will consume fewer IP addresses (not to mention fewer host resources) than you would if each user could launch an unlimited number of virtual desktops.
I also recommend adopting an automated IP address management tool. There are a number of third-party options on the market. Windows Server 2012 and 2012 R2 also included IP address management software in the Microsoft IPAM feature.
Like any other form of resource consumption, IP address usage tends to evolve over time. To that end, it is extremely important to track IP address usage over the long term so you can project if or when your IP address pools are in danger of depletion.
An IP address management tool should also include an alerting mechanism that responds to situations where a DHCP pool runs low on addresses; the depletion of a DHCP scope can result in a service outage for some users. Using an automated software application to track scope usage is the best way to make sure that you are never caught off guard.
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