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What are RDS CALs and how should IT use them?

IT teams rely on CALs to ensure that RDS users are properly licensed for their sessions, so they should know how to work with them and what different options they present.

As an IT professional, Microsoft licensing rules can be the bane of your existence if you're using RDS, so it's important to get your licenses and policies straight.

Prior to the release of Windows Server 2008 R2 in 2009, if you used Terminal Services -- now Remote Desktop Services -- you had to purchase Terminal Services licenses for Windows Terminal Server to meet licensing requirements for remote sessions. Since Microsoft released Windows Server 2008 R2, however, you must comply with an RDS licensing scheme based on the Remote Desktop (RD) Licensing role for Windows Server instead. This remains true through the most current preview of Windows Server 2022.

Make sure you understand the requirements of the RD Licensing policy and the various methods to calculate the number of licenses you require to comply with RDS licensing terms and conditions.

What are RDS CALs and who needs to use them?

Each active remote session on a server that supports the RD Session Host (RDSH) services role requires a single RDS Client Access License (CAL). Every prospective user needs a unique CAL to create a working remote session to any targeted RDSH server.

RDS per-device CALs
How Microsoft Remote Desktop Services per-device Client Access Licenses work

RDS CALs must be tracked across an organization's networks through the Windows Server Licensing role. That licensing role keeps track of CALs on a network and won't allow more active sessions at a given time than the total number of CALs under its control. Microsoft Learn offers an excellent tutorial on this subject.

Any current Windows Server -- namely 2016, 2019 and 2022 -- includes the two server-side building blocks. Administrators need to set up and use RDSH and RD Licensing services.

How does the RDS licensing model work?

There are two major components that come into play with remote desktop access in a Microsoft RDS deployment apart from the CALs.

Remote Desktop Session Host

For Windows Server 2008 R2 and later versions, the server role for RDS is called RDSH. For clients to have a remote server with which to establish a session, at least one internet-accessible host on the network must support the RDHS server role.

Licensing server

When it comes to RDS licensing, at least one RD Licensing server must also be available on your network -- usually as part of the domain or domain forest in which the remote users reside. It is possible for a single physical or virtual server to support both the RDSH and the RD Licensing role services -- usually called an RD Licensing server -- in smaller network deployments. On larger, more distributed networks, those roles typically reside on different servers, often in different locations.

Types of RDS CALs: per device vs. per user

While the purpose for all CALs is the same, there are different approaches to these licenses. CALs come in two forms:

  1. RDS per-device CALs. These licenses are associated with a specific device. They are nontransferable to other devices.
  2. RDS per-user CALs. These licenses are associated with a specific user account. They are nontransferable to other user accounts.

Choosing one type of CAL over another depends on whether users typically initiate remote sessions from the same device or not. If they generally use the same device, then per device probably makes the most sense. On the other hand, if users log in remotely from two or more devices regularly, per-user RDS licensing keeps costs down.

To determine the exact needs for an organization's CALs, IT teams should calculate the maximum number of simultaneous remote sessions needed.

Calculating CAL needs

To determine the exact needs for an organization's CALs, IT teams should calculate the maximum number of simultaneous remote sessions needed. This straightforward number should determine how many CALs are necessary for any RD Licensing server to manage.

Microsoft sells its RDS CALs on an individual basis or in license packages of five and 25. The company negotiates some set number of CALs as part of overall volume licensing agreements. Prices for CALs vary from around $120 -- purchased one at a time or in small lots -- down to $100 or so for 25-pack CALs. Organizations with a volume licensing program agreement and business leaders have to negotiate with Microsoft on a case-by-case basis. Generally speaking, negotiating volume pricing beats unit prices for the various RDS CAL bundles available through resellers for one, five, 10 and 25 packs.

Tips for implementing RDS licensing

When an IT team sets up one or more Windows 2016, 2019 or 2022 server for the RDSH and RD Licensing services roles, a grace period of 60 days, renewable once for a total of 120 days, applies to the initial usage time frame for client access. During this time, Microsoft does not check CALs. Once that grace period expires, however, some IT administrators report difficulties recognizing their RD Licensing server, which locks remote clients out of remote access.

This is a well-known catch that administrators can repair by deleting a specific registry key. Once the admin deletes that key, remote clients can then use the RD Licensing server to access remote desktop sessions using available CALs.

RDS also supports VDI deployments. In a VDI deployment, every device that connects to RDS must have its own RDS CAL and access to a license server, as with any remote desktop access. In addition, organizations must either be covered by Windows Client Software Assurance or a license for Windows Virtual Desktop Access to use remote desktop on a VDI desktop.

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