STUN Server Connectivity - AVD Test

Connections to Azure Virtual Desktop use Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). RDP Shortpath is a feature of Azure Virtual Desktop that establishes a direct UDP-based transport between a supported Windows Remote Desktop client and session host. By default, Remote Desktop Protocol (RDP) tries to establish connection using UDP and uses a TCP-based reverse connect transport as a fallback connection mechanism. TCP-based reverse connect transport provides the best compatibility with various networking configurations and has a high success rate for establishing RDP connections. UDP-based transport offers better connection reliability and more consistent latency. RDP Shortpath can be used in both Managed Networks and Public networks.

When used in Public networks, direct connectivity is established between the client and the session host using a public connection. There are two connection types when using a public connection. Both these types are explained as follows:

  • A direct UDP connection using the Simple Traversal Underneath NAT (STUN) protocol between a client and session host.

  • An indirect UDP connection using the Traversal Using Relay NAT (TURN) protocol with a relay between a client and session host.

The transport used for RDP Shortpath is based on the Universal Rate Control Protocol (URCP). URCP enhances UDP with active monitoring of the network conditions and provides fair and full link utilization.

RDP Shortpath extends RDP multi-transport capabilities. Initial session brokering is managed through the Azure Virtual Desktop service and the reverse connect transport. RDP Shortpath is established after authentication, and if successfully established, the reverse connect transport is dropped and all traffic flows over the RDP Shortpath.

In some environments, administrators may block UDP on the direct VPN connection and hence, the users may have to use the ICE/STUN protocol to establish a connection over the public network. If the STUN server fails to establish the connection with the user, then, the user may not be able to establish the connection to the session hosts / AVD. This may highly impact the user experience on the Azure infrastructure. To ensure that the users establish connections to the session hosts / AVD seamlessly through STUN servers, it is essential for the administrators to monitor the connectivity of the STUN server periodically. The STUN Server Connectivity - AVD test helps administrators in this regard.

With the help of this test, administrators can identify those STUN servers through which users failed to establish connection to the session hosts / AVD. The message displayed as part of detailed diagnostics helps administrators troubleshoot connection issues encountered by the users through STUN servers.

Target of the test : Azure Virtual Desktop

Agent deploying the test : An internal agent

Outputs of the test : One set of results will be reported for each STUN Server connected to the chosen Session Host / AVD

Configurable parameters for the test
Parameters Description

Test period

This indicates how often should the test be executed.

Host

The host for which the test is to be configured.

Port

The default port is NULL.

DD Frequency

Refers to the frequency with which detailed diagnosis measures are to be generated for this test. The default is 1:1. This indicates that, by default, detailed measures will be generated every time this test runs, and also every time the test detects a problem. You can modify this frequency, if you so desire. Also, if you intend to disable the detailed diagnosis capability for this test, you can do so by specifying none against DD frequency.

Detailed Diagnosis

To make diagnosis more efficient and accurate, the eG Enterprise embeds an optional detailed diagnostic capability. With this capability, the eG agents can be configured to run detailed, more elaborate tests as and when specific problems are detected. To enable the detailed diagnosis capability of this test for a particular server, choose the On option. To disable the capability, click on the Off option.

The option to selectively enable/disable the detailed diagnosis capability will be available only if the following conditions are fulfilled:

  • The eG manager license should allow the detailed diagnosis capability
  • Both the normal and abnormal frequencies configured for the detailed diagnosis measures should not be 0.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

STUN server status

Indicates the current status of this STUN server.

 

The measure values that this test can report and their corresponding numeric values are listed in the table below:

Note:

By default, this measure reports the above-mentioned values to indicate the current status of each STUN server. In the graph of this measure however, the same is represented using the numeric equivalents i.e., 0 or 1.

The detailed diagnosis reported for the Summary descriptor of this measure lists the messages from the STUN servers.