XenServer 5.6 now supports Citrix centralized licensing.

Citrix XenServer 5.6 now supports Citrix centralized licensing for all paid editions of the product. In XenServer Advanced, Enterprise, and Platinum Editions, customers must allocate their licenses using a Citrix License Server, just as with other Citrix components. With this change, license allocation is managed centrally and enforced by a standalone Citrix license server (physical or virtual) in your environment.

Because this is a significant change, Citrix recommends all paid XenServer customers perform these three steps prior to upgrading to XenServer 5.6:

Verify your license entitlement in MyCitrix and ensure that you have an appropriate number of licenses to support your existing XenServer deployment.
If you already have a Citrix License Server, verify the hostname of that license server. Otherwise, download Citrix License Server software from MyCitrix and configure it on a physical or virtual host.
Download your new .LIC license file and apply it to your Citrix Licensing Server.

Once these steps are complete, you can safely upgrade your existing XenServer deployment to version 5.6.

Product Editions

Q: How does this licensing change impact Free XenServer users?

A: There is no impact to free XenServer users. Free XenServer continues to use our file based .XSLIC license format, which remains unchanged in 5.6. Upgrades from XenServer 5.5 (Free) to XenServer 5.6 (Free) are unaffected by these changes.

Q: How is free XenServer licensed?

A: Free XenServer users will continue to download a license file in .XSLIC format and apply it to each individual host in their pool. As in previous versions, under the Free XenServer EULA, contact and usage information must be updated annually. On or before the one year expiration, administrators must log on and update their information to obtain a new one year free license file.

Q: How is paid XenServer licensed?

A: Paid editions of XenServer (Advanced, Enterprise, and Platinum) now require the download of a new .LIC license key. This license key is hosted on a central Citrix License Server, and each XenServer host checks out a license at boot time. You can see your server count entitlement in the MyCitrix portal, and you can allocate these licenses among your servers. An individual .LIC file contains not only authorization for multiple components of XenServer, but can authorize multiple hosts as well.

Q: How does this change benefit existing (paid) XenServer customers?

A: Moving to the Citrix centralized licensing model allows administrators to centralize their licensing for all Citrix Products. The License Management Console gives a quick view of the entitlement and current allotment of licenses, enabling administrators to stay in compliance and view all their Citrix product usage in a single location.

Q: What happened to Essentials for XenServer? Did my feature set change?

A: There have been some packaging and naming changes in the XenServer 5.6 release. In addition to the free XenServer platform, Citrix now offers XenServer Advanced, Enterprise, and Platinum. XenServer Advanced is a new lower-priced offering with this release. Existing Essentials for XenServer Enterprise customers will transition to XenServer Enterprise, and existing Essentials for XenServer Platinum customers will transition to XenServer Platinum.

Q: What if I already upgraded my XenServer hosts? What do I do now?

A: If you upgrade a previous licensed edition of Essentials for XenServer to XenServer 5.6, the installer will detect the presence of your previous paid license, and put your hosts into a 30 day grace period. During this time, XenServer Enterprise functionality is available. You have until the end of the grace period to configure a Citrix License Server and download the new license file.

Q: What if my grace period expires? Will I lose my virtual machines?

A: XenServer will never cause you to lose valuable virtual machine data. If a license is not available, XenServer will revert to its original unregistered state – and require the administrator to apply either a Free or Paid license to the host before allowing VM power on/off operations. If the grace period has expired, registering your XenServer as a free product will allow you basic platform functionality while you obtain the correct licenses.

Q: What if I want to expand my existing XenServer 5.5 (or earlier) environment?

A: Although we would encourage all customers to upgrade to XenServer 5.6, Citrix will continue to provide .XSLIC license keys until XenServer 5.5 has reached End-of-Life status. XenServer 5.5 and earlier will continue to operate on the .XSLIC, individually-licensed-server model.

Q: What about XenDesktop customers?

A: XenDesktop customers are entitled to use XenServer to host any of their virtual desktops and XenDesktop infrastructure. For instance, XenServer can be used to host Windows XP, Vista or Win7 virtual desktops, as well as the XenApp and XenDesktop support virtual machines for the environment. However, the same XenServer environment may not be used to host overall infrastructure (domain controllers, DNS, etc.) or other general purpose IT workloads. These hosts should be maintained in a separate pool from other XenServer hosts, as mixing license types is not supported.

License Server and Enforcement

Q: How do existing Essentials for XenServer customers obtain license files?

A: Existing customers who purchased Essentials for XenServer Enterprise or Platinum editions, and who installed components from the Essentials range (such as StorageLink, Workload Balancing, Lab Manager, Stage Manager) will be familiar with redeeming licenses from My Citrix, and the need for a standalone license server to be present in their environment.

These customers should return to My Citrix and re-host their existing license key to obtain an updated key that can be used to license XenServer 5.6. For instructions on how to re-host license keys, see article CTX118324 - How to Return/re-host a License using MyCitrix.

Customers who purchased Essentials for XenServer, but did not redeem their license key from My Citrix (using the Web key) must locate the Web key and use it at My Citrix. If you purchased Essentials for XenServer, but are no longer in possession of the Web key, contact customer service for assistance in locating your license on MyCitrix.

Q: Can I use an existing Citrix License Server for XenServer?

A: YES. If you have an existing license server, the transition to v6 licensing in XenServer dramatically simplifioes your license management. Just upload your XenServer license, and point your XenServer hosts at the IP or Hostname of your license server.

Q: I have never used a Citrix License Server. How and where do I download Citrix License Server software?

A: XenServer requires the Citrix License Server 11.6.1 or later. The windows license server can be downloaded from MyCitrix or at the following location: http://www.citrix.com/english/ss/downloads/details.asp?downloadId=1688507&productId=1679389.

Documentation for the Citrix License Server is available at edocs, here:

http://support.citrix.com/proddocs/index.jsp?topic=/licensing-1161/lic-licensing-1161.html

Configuration of the license server is straightforward and a single license server can be shared among all Citrix products.

Q: Can I run the license server as a virtual machine?

A: YES. Your windows license server can run as a virtual machine in your XenServer environment. License grace periods and check-out algorithms support this use case in any size environment.

Q: Can I use the XenServer Platinum Evaluation Virtual Appliance?

A: Temporarily. The XenServer Evaluation Virtual Appliance( EVA) is preconfigured with a Citrix License Server up and running for demonstration purposes. However, the Microsoft EULA does not permit long term use of this virtual machine in production.

Q: What if I do not have Windows servers in my environment? Is there an alternate way to set up a Citrix license server?

A: A Linux-based license server virtual appliance will be available from Citrix in June, 2010. This appliance will have minimal configuration and allow customers to bring up a license server in about five minutes.

Q: How has enforcement changed in this release?

A: Previous versions of XenServer did not aggressively enforce server count restrictions. With version 5.6 and the centralized licensing model, each individual XenServer host checks out a license from the license server. It is important to verify your license entitlement and actual usage before upgrading to XenServer 5.6 to avoid potential downtime.

Licensing your XenServer Pool

Q: How do I apply a license to all my hosts?

A: Inside XenCenter 5.6, go to Tools > License Manager:

Select the hosts you would like to license, and then click Assign License:

In the Apply License dialog, specify the license type you wish to assign to the host, and enter the hostname or IP address of your Citrix License Server.

Essentials for XenServer components

Q: In Essentials for XenServer 5.5, I had to manage multiple license types and locations for my individual components. Is this still the case?

A: No. In XenServer 5.6, customers will download a single XenServer license file. Each component of XenServer will either directly or indirectly query the license server for authorization and activate if appropriate. You will only have a single XenServer license file, which contains information about the total number of hosts you may activate and the individual components included in your entitlement.

Q: What about StorageLink Licensing?

A: StorageLink queries the license server, and upon finding a XenServer Enterprise or Platinum license, activates the appropriate feature set. There is no need to maintain a separate StorageLink license.

Q: Do Lab and Stage Manager still need to be licensed separately?

A: No. In previous editions, Lab and Stage Manager required individual licenses to be applied. With XenServer 5.6, Lab and Stage Manager query their XenServer host for their activation rights, which are included inside your XenServer Platinum license. There is no need to manage separate licenses for Lab and Stage Manager. If you are an existing Lab or Stage Manager customer, Citrix recommends first upgrading XenServer, and then upgrading Lab or Stage Manager immediately afterward. Lab and Stage Manager 5.6 pick up their new license from XenServer directly.

Other Questions

Q: Can I mix license types in the same pool of servers? (For instance, XenServer Enterprise and XenServer Platinum, or XenServer Platinum and XenServer for XenDesktop?)

A: Mixing license types inside a single XenServer pool is not supported. A single license server can contain multiple license types, but each pool should maintain license consistency across all hosts.

Q: How can customers obtain XenServer Platinum Evaluation Licenses?

A: XenServer Platinum 90 day Evaluation Licenses are available at www.citrix.com/xenserver.

Q: How do partners obtain Internal Use or Evaluation Licenses?

A: Partners can obtain internal use or evaluation licenses from the standard MyCitrix distribution methods. Note that Lab and Stage Manager cannot be licensed for internal use, so Internal Use licenses are currently restricted to XenServer Enterprise.

Source :  http://support.citrix.com/article/CTX125301