5.8

limitation.
DCOM is also the lowest common protocol used for installing the Agent and for collecting data.
Uninstalling and upgrading the Agent are not bound by this limitation.
If the Collector lists an Agent as listening with HTTP when communicating with the Agent, and the
HTTP connection cannot be established, DCOM communication is attempted.
Communication Protocol Change Process
A change protocol request is applied when you change the protocol the Collector uses to communicate
with an Agent on a Windows machine. The supported communications protocols are HTTP and DCOM.
DCOM is the oldest supported protocol and dates back to the VCM 3.0x.
HTTP protocol was introduced with VCM4.5. A change protocol request makes the following changes.
n When changing the protocol from DCOM to HTTP, the EcmComSocketListenerService module is
deployed and run.
n When changing from HTTP to DCOM, the EcmComSocketListenerService is removed.
To troubleshoot problems related to communication protocols, review the job history, identify the step
that failed, and determine what might be impeding communication protocol change process.
Detect Previous Install
The detect previous install action evaluates the target Windows machine to determine whether a previous
version of the VCM Agent is installed.
When you install the VCM 4.11.x Agent or later, if a previous Agent version is detected, it must be
removed.
The detect previous install action determines if a previous Agent is present by attempting to connect to the
Agent installation DCOM components, the Basic and Agent Installers. If a connection is made to either of
these components, the detect previous install action sets a state member that the Validate Installation
Environment, Interrogate Target Environment, and Resolve Uninstall Dependencies actions use to
determine if they should run.
These actions remove the previous Agents and are included in all types of install and uninstall requests.
Uninstall Agent
The uninstall Agent action removes all product modules that must be uninstalled from the target Windows
machine before installing the new communication protocol modules.
1. A list of product modules is obtained from the database.
2. A connection is made to the module installer.
3. The runtime Agent lock is updated.
4. Each module is uninstalled in turn by the module installer.
A failure in this action causes the installation to fail.
Uninstall Package Installer
The uninstall package installer action completes the removal of the previous communication protocol
modules in preparation for the new modules.
VCM Troubleshooting Guide
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