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 Solaris LDoms server

Agent deploying the test : An internal agent

Outputs of the test : One set of results for each powered-on guest on the Solaris LDoms server being monitored.

Configurable parameters for the test
Parameter Description

Test period

How often should the test be executed

Host

The host for which the test is to be configured.

Port

The port number at which the specified host listens. By default, the port is NULL.

Domain

Specify the domain within which the virtual guests reside. Since the Solaris LDoms server supports only Solaris and Linux guests, this parameter should always be set to none.

Admin User

This test connects to each virtual guest and collects status and resource usage statistics from the guest. In order to do so, the test must be configured with user privileges that allow a remote connection to the virtual guest from the Solaris host. If a single user has access to all the guest domains on the Solaris server, specify the name of that user against Admin User, and specify his password against Admin Password. On the other hand, if the user credentials vary from one guest to another, then multiple Admin Users and Admin Passwords might have to be specified for every Solaris LDoms server being monitored.

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 Click here hyperlink that appears just above the parameters of this test in the test configuration page. To know how to use the special page, refer to Configuring Users for VM Monitoring.

Admin Password

The password of the Admin User needs to be provided here. Here again, if multiple passwords need to be specified, then follow the procedure detailed in Configuring Users for VM Monitoring.

Confirm Password

Confirm the password by retyping it here. Here again, if multiple passwords need to be confirmed, then follow the procedure detailed in Configuring Users for VM Monitoring.

Measurements made 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.