SCOM: Locally Monitoring a Listening TCP Port
August 13, 2009 3 Comments
Typically, one would monitor a TCP port remotely, from a designated watcher node, as a means of confirming availability of a network service, but in some cases, this may not be the most desirable method to poll for TCP port status. For example, if you wanted to monitor the availability of tcp port on a large number of servers that are SCOM agent-managed systems, where you are concerned with the availability of the particular port only when the rest of the system is functioning normally, it may make more sense to monitor this port status locally from the agent. This minimizes the number of false alarms (each time the monitored nodes are taken down for maintenance, the remote monitor will throw alerts) and also makes deployment much easier (simply target groups for overrides to enable the monitor).
A simple VBS script that calls portqry.exe (from the Windows Support Tools) or “netstat –an” and parses the output to confirm port listening status can fulfill the monitoring role in this scenario. I wrote such a script that will use netstat –an to check the TCP ports currently in a listening state on the localsystem and parse the output to determine that the defined TCP port is in a listening state.
The core logic can be seen in this excerpt:
sCmd = “netstat -an -proto TCP”
set objShell = createobject(“wscript.shell”)
set objExec = objShell.exec(sCmd)
set oStdOut = objExec.stdoutbl_Healthy = false
Do until oStdOut.AtEndofStream
sLine = “”
sLine = oStdOut.ReadLine
if instr(sLine, “LISTENING”) > 0 and instr(sLine,”:” & nPortToCheck) then
bl_healthy = true
end if
loop
The full script can be downloaded here (this is provided as-is, with no guarantee of function or support, test before deploying, etc).
Walkthrough on creating a corresponding Unit Monitor behind the cut
Operating-Quadrant 