TCP Traffic - VM Test

Since most popular applications rely on the TCP protocol for their proper functioning, traffic monitoring at the TCP protocol layer can provide good indicators of the performance seen by the applications that use TCP. The most critical metric at the TCP protocol layer is the percentage of retransmissions. Since TCP uses an exponential back-off algorithm for its retransmissions, any retransmission of packets over the network (due to network congestion, noise, data link errors, etc.) can have a significant impact on the throughput seen by applications that use TCP. This test monitors the TCP protocol traffic to and from a guest, and particularly monitors retransmissions.

Target of the test : A Hyper-V / Hyper-V VDI server

Agent executing the test : An internal agent

Output of the test : For a Hyper-V server, one set of results will be reported for every powered-on VM on the server.

For a Hyper-V VDI server, one set of results will be reported for the user who is currently logged into each virtual desktop on the server

Configurable parameters for the test
  1. Test period - How often should the test be executed
  1. Host - The host for which the test is to be configured.
  2. port - The port at which the host listens. By default, this is NULL.

  3. inside view using - By default, this test communicates with every VM remotely and extracts “inside view” metrics. Therefore, by default, the inside view using flag is set to Remote connection to VM (Windows).

    Typically, to establish this remote connection, eG Enterprise requires that the eG agent be configured with domain administrator privileges. In high-security environments, where the IT staff might have reservations about exposing the credentials of their domain administrators, this approach to extracting “inside view” metrics might not be preferred. In such environments therefore, eG Enterprise provides administrators the option to deploy a piece of software called the eG VM Agent on every Windows VM; this VM agent allows the eG agent to collect “inside view” metrics from the Windows VMs without domain administrator rights. Refer to Configuring Windows Virtual Machines to Support theInside View Using the eG VM Agent for more details on the eG VM Agent. To ensure that the “inside view” of Windows VMs is obtained using the eG VM Agent, set the inside view using flag to eG VM Agent (Windows). Once this is done, you can set the domain, admin user, and admin password parameters to none.

  1. domain, admin user, admin password, and confirm password – By default, this test connects to each virtual guest remotely and attempts to collect “inside view” metrics. Accordingly, the inside view using flag is set to Remote connection to VM (Windows) by default. To obtain a remote connection, the test must be configured with the privileges of an administrative user to the domain within which the guests reside. The first step towards this is to specify the DOMAIN within which the virtual guests reside. The admin user and admin password will change according to the domain specification. Discussed below are the different values that the domain parameter can take, and how they impact the admin user and admin password specifications:

    • If the VMs belong to a single domain:  If the guests belong to a specific domain, then specify the name of that domain against the domain parameter. In this case, any administrative user in that domain will have remote access to all the virtual guests. Therefore, an administrator account in the given domain can be provided in the ADMIN USER field and the corresponding password in the ADMIN PASSWORD field. Confirm the password by retyping it in the CONFIRM PASSWORD text box.
    • If the VMs belong to different domains: In this case, you might want to provide multiple domain names. If this is done, then, to access the guests in every configured domain, the test should be configured with the required user privileges; this implies that along with multiple DOMAIN names, multiple ADMIN USER names and ADMIN PASSWORDs would also have to be provided. To help administrators provide these user details quickly and easily, the eG administrative interface embeds a special configuration page. To access this page, simply click on the encircled '+' icon that appears alongside the . To know how to use the special page, refer to Configuring Users for VM Monitoring.
    • If the inside view using flag is set to ‘eG VM Agent (Windows)’: On the other hand, if the inside view using flag is set to eG VM Agent (Windows), then it implies that the inside view can be obtained without domain administrator privileges. Therefore, set the domain, admin user, and admin password parameters to none.
  2. segments sent min - Specify the minimum threshold for the number of segments sent/transmitted over the network. The default value is 10; in this case, the test will compute/report the Retransmit ratio from VM measure only if more than 10 segments are sent over the network – i.e., if the value of the Segments sent by VM measure crosses the value 10. On the other hand, if the Segments sent by VM measure reports a value less than 10, then the test will not compute/report the Retransmit ratio from VM measure. This is done to ensure that no false alerts are generated by the eG Enterprise system for the Retransmit ratio from VM measure. You can change this minimum threshold to any value of your choice.
  3. REPORT BY USER – For the Hyper-V monitoring model, the REPORT BY USER flag is set to NO by default, indicating that by default, the guest operating systems on the Hyper-V server are identified using the hostname specified in the operating system. On the other hand, for the Hyper-V VDI model, this flag is set to YES by default; this implies that in case of VDI servers, by default, the guests will be identified using the login of the user who is accessing the guest OS. In other words, in VDI environments, this test will, by default, report measures for every username_on_virtualmachinename.

  4. REPORT POWERED OS - This flag becomes relevant only if the report by user flag is set to ‘Yes’.

    If the report powered os flag is set to Yes (which is the default setting), then this test will report measures for even those VMs that do not have any users logged in currently. Such guests will be identified by their virtualmachine name and not by the username_on_virtualmachinename. On the other hand, if the report powered os flag is set to No, then this test will not report measures for those VMs to which no users are logged in currently. 

  5. ignore vms inside view - Administrators of some high security Hyper-V environments might not have permissions to internally monitor one/more VMs. The eG agent can be configured to not obtain the 'inside view' of such ‘inaccessible’ VMs using the ignore vms inside view parameter. Against this parameter, you can provide a comma-separated list of VM names, or VM name patterns, for which the inside view need not be obtained. For instance, your ignore vms inside view specification can be: *xp,*lin*,win*,vista. Here, the * (asterisk) is used to denote leading and trailing spaces (as the case may be). By default, this parameter is set to none indicating that the eG agent obtains the inside view of all VMs on a Hyper-V host by default.

    Note:

    While performing VM discovery, the eG agent will not discover the operating system of the VMs configured in the ignore vms inside view text box.

  6. exclude vms - Administrators of some virtualized environments may not want to monitor some of their less-critical VMs - for instance, VM templates - both from 'outside' and from 'inside'. The eG agent in this case can be configured to completely exclude such VMs from its monitoring purview. To achieve this, provide a comma-separated list of VMs to be excluded from monitoring in the exclude vms text box. Instead of VMs, VM name patterns can also be provided here in a comma-separated list. For example, your exclude vms specification can be: *xp,*lin*,win*,vista. Here, the * (asterisk) is used to denote leading and trailing spaces (as the case may be). By default, this parameter is set to none indicating that the eG agent obtains the inside and outside views of all VMs on a virtual host by default. By providing a comma-separated list of VMs/VM name patterns in the exclude vms text box, you can make sure the eG agent stops collecting 'inside' and 'outside' view metrics for a configured set of VMs.
  7. ignore winnt – By default, the eG agent does not support the inside view for VMs executing on Windows NT operating systems. Accordingly, the ignore winnt flag is set to Yes by default.
Measurements reported by the test
Measurement Description Measurement Unit Interpretation

Segments received by VM

Indicates the rate at which segments are received by the guest.

Segments/Sec

 

Segments sent by VM

Indicates the rate at which segments are sent to clients
or other guests

Segments/Sec

 

Retransmits by VM

Indicates the rate at which segments are being retransmitted by the guest

Segments/Sec

 

Retransmit ratio from VM

Indicates the ratio of the rate of data retransmissions to the rate of data being sent by the guest

Percent

Ideally, the retransmission ratio should be low (< 5%). Most often retransmissions at the TCP layer have   significant impact on application performance. Very often a large number of retransmissions are caused by a congested network link, bottlenecks at a router causing buffer/queue overflows, or by lousy network links due to poor physical layer characteristics (e.g., low signal to noise ratio). By tracking the percentage of retransmissions at a guest, an administrator can quickly be alerted to problem situations in the network link(s) to the guest that may be impacting the service performance.