Citrix 3 4 VDA

A XenDesktop site is made of many components: hypervisors, server OS instances, Delivery Controllers, License Server and so on. The keystone that lets all those moving parts work together is the Virtual Delivery Agent, the VDA. The VDA is the software you install on every virtual or physical machine running a Windows server or desktop operating system that you want to publish as a resource to your users.

Once the VDA is installed, it communicates with the Delivery Controller through the FMA stack, while the Receiver software installed on the client device communicates with the VDA over the ICA/HDX protocol. When the connection is internal, the VDA and Receiver establish a direct end-to-end connection. When the connection is external, traffic flows from the client to NetScaler Gateway, then from NetScaler to the internal network and finally to the VDA. If the client does not have a Receiver installed, the HTML5 web Receiver embedded in StoreFront takes over.

Where to install a VDA

  • On virtual desktops (Windows 7, 8, 10) used for VDI scenarios.
  • On server OS instances (Windows Server 2008 R2, 2012 R2) used for hosted shared apps and desktops.
  • On physical PCs for the Remote PC use case.

The VDA also makes efficient use of GPU and graphics features when needed (HDX 3D), which is essential for graphics-intensive use cases. In the next video we will discuss the FrameHawk acquisition and what it brings to the protocol stack.

Summary

The Citrix Virtual Delivery Agent (VDA) is a critical component installed on virtual and physical machines running Windows Server or desktop operating systems. It communicates with the Delivery Controller to enable users to access remote desktops and applications through Citrix Receiver clients. Clients establish direct connections with VDA in local networks, while external connections are tunneled securely through designated ports, and HTML5 Receiver provides browser-based access when the client software is unavailable.

Key points

  • VDA (Virtual Delivery Agent) is installed on every virtual or physical machine delivering desktops or applications
  • VDA communicates with the Delivery Controller using ISER protocol to manage client connections
  • Citrix Receiver (or HTML5 Receiver) is installed on client machines to connect to VDA
  • Direct connections between Receiver and VDA occur within local networks without additional overhead
  • External connections are tunneled securely through designated ports (e.g., port 443) for safety and NAT traversal
  • The architecture enables efficient resource utilization and optimized graphics delivery for remote desktop users

FAQ

What is the Virtual Delivery Agent (VDA) and what does it do?

VDA is a core Citrix component installed on machines (virtual or physical) running Windows Server or desktop operating systems. It communicates with the Delivery Controller to manage connections and allow end-users to access remote desktops and applications through Citrix Receiver clients.

How do clients connect to VDA, and what are the connection types?

Clients install Citrix Receiver software to connect to VDA. Within a local network, Receiver and VDA establish direct connections for optimal performance. External clients tunnel connections through secure ports (443) via the delivery infrastructure. If Receiver is unavailable, HTML5 Receiver provides browser-based access.

What's the role of the Delivery Controller in relation to VDA?

The Delivery Controller communicates with VDA using the ISER protocol to broker connections between clients and resources, manage user sessions, handle authentication, and coordinate the delivery of virtual desktops and applications.