VB Script to snoop DHCP logs
by, 1st February 2013 at 05:39 PM (14944 Views)
A forum post got me to thinking about a script to parse DHCP logs to notify someone when a particular MAC checks in with the server. You can run this script as a reoccurring task on the DHCP server and when it finds a match for the desired MAC it will send an email regarding the activity. This script will also keep a log of its own to prevent multiple email messages for the same log entry it finds. I've run this in a production environment with an internally hosted Exchange server and it works. You may need to debug a little depending on your environment.
The On Error Resume Next line in the email function is to prevent the script from hanging if there is an error with the mail server. If that were to happen without it there instances of wscript.exe would keep spawning and never exit each time the scheduled task would fire.
Code:Call Main Sub Main 'MAC to find strFindMAC = "xxxxxxxxxxxx" Set objFSO = CreateObject("Scripting.FileSystemObject") Const ForReading = 1 Const ForWriting = 1 'Determine log name based on day of week strLogPath = "c:\windows\system32\dhcp\" strWeekDay = weekdayname(weekday(date)) strFullLogPath = strLogPath & "DhcpSrvLog-" & Left(strWeekday,3) & ".log" 'Check to see if log exists If objFSO.FileExists(strFullLogPath) Then 'Do Nothing Else WScript.Quit End If 'Open DHCP log file for reading Set objDHCPLogFile = objFSO.OpenTextFile(strFullLogPath, ForReading) 'Copy file contents into string strDHCPLogFile = objDHCPLogFile.ReadAll objDHCPLogFile.Close 'Break into individual lines arrLines = Split(strDHCPLogFile,vbCrLf) 'Loop through the array and build another array of lines that contain the MAC For Each strLine in arrLines If InStr(strLine, strFindMAC) Then intCount = intCount + 1 ReDim Preserve arrFound(intCount) arrFound(intCount) = strLine End If Next 'If no matches are found then abort the script If intCount = 0 Then WScript.Quit End If 'Get the last line of matching MAC log entries strLastLine = arrFound(intCount) 'Split the log entry on commas and dump to array arrLastLine = Split(strLastLine, Chr(44)) 'Format message strDate = arrLastLine(1) strTime = arrLastLine(2) strAction = arrLastLine(3) strIPAddress = arrLastLine(4) strHostName = arrLastLine(5) strMessage = "MAC address " & strFindMAC & " has checked into the DHCP server on " & strDate & " at " & strTime & "." & Chr(13) _ & strIPAddress & " was " & strAction & "ed" & " to hostname " & strHostName & "." 'This next block of code will read/write a log for the script itself. This will prevent the script from sending multiple 'emails for the same DHCP log entry. 'Check to see if script log exists If objFSO.FileExists("DHCPScriptLog.txt") Then 'Read log and get the time Set objScriptLogFile = objFSO.OpenTextFile("DHCPScriptLog.txt", ForReading) strLastTime = objScriptLogFile.ReadAll objScriptLogFile.Close 'If the last time matches the time pulled from the DHCP log then quit the script If strLastTime = strTime Then WScript.Quit End If End If 'Write the log file Set objScriptLogFile = objFSO.CreateTextFile("DHCPScriptLog.txt", ForWriting) objScriptLogFile.Write strTime objScriptLogFile.Close 'Call the email function to send the message Email(strMessage) End Sub Function Email(strMessage) On Error Resume Next Set objMessage = CreateObject("CDO.Message") objMessage.Configuration.Fields.Item("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2 objMessage.Configuration.Fields.Item("http://schemas.microsoft.com/cdo/configuration/smtpserver") = "mail.domain.com" objMessage.Configuration.Fields.Item("http://schemas.microsoft.com/cdo/configuration/smtpserverport") = 25 objMessage.Configuration.Fields.Update objMessage.Subject = "DHCP Log Script" objMessage.From = "DHCPScript@domain.com" objMessage.To = "firstname.lastname@example.org" objMessage.TextBody = strMessage objMessage.Send End Function
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