Knowledge Base Detailed Resolution

Category:

ipMonitor - Monitoring

Question:

Why does the NETSTAT -A command list so many TCP/IP connections?

Resolution:

Running a "NETSTAT -A" command from the command prompt shows a large number of TCP/IP connections established by the ipMonitor software. This increased network traffic can affect ipMonitor's ability to create new connections, especially since many existing TCP/IP connections remain in a reserved TIME_WAIT state. Ultimately, if ipMonitor is unable to open new connections, monitor failures can occur.

Cause

The majority of TCP/IP connections displayed are ephemeral ports that have already been closed, but that remain reserved before they can be reused. This reserved state is denoted by the netstat TIME_WAIT label.

Microsoft limits the number of connections to 3975 by default, meaning that there can only be 3975 TCP/IP connections open at any given time. In addition, the TIME_WAIT state is configured by default to be 240 seconds. This means that Windows can only support an average of 33 TCP/IP connections per second. ipMonitor must then wait 240 seconds before being able to reuse those connections. If you have a large number of configured Monitors set to retest resources at short intervals, 3975 connections every 4 minutes may simply not be enough.

Solution

Attempt the following troubleshooting steps in the listed order:

• Increase the refresh time between monitor tests.
• Increase the maximum simultaneous connections.
• Reduce the duration of the reserved state.

Warning! Windows registry changes can result in severe system damage if performed incorrectly. Before you modify the registry, make a backup copy and ensure you understand how to restore the registry if a problem occurs. For information regarding backing up, restoring, and editing the registry, refer to the Microsoft Knowledge Base.

Increase the Refresh Time between Monitor Tests

If possible, we suggest configuring your Monitors to use the default value of 300 seconds between Monitor tests. This optimal setting ensures there are enough TCP connections available when needed.

Increase the Maximum Simultaneous Connections

1. Start the Registry Editor (Regedt32.exe)

2. Access the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

3. Add a DWORD value to this registry key:

4. Exit the Registry Editor.

Reduce the Duration of the Reserved State

Reducing the value of the TIME_WAIT state results in TCP connections being reused faster, therefore allowing for an increased number of connections during the same length of time. Note that if the value is too low, the TCP connection may close before Monitor testing is complete.

To reduce the duration of the reserved state:

1. Start the Registry Editor (Regedt32.exe)

2. Access the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

3. Add a DWORD value to this registry key:

4. Exit the Registry Editor.