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14.3 Server ClassesNearly 50 different settings can be configured on a Microsoft DNS Server. They range from scavenging and logging settings to settings that customize the name server's behavior, such as how zone transfers are sent to secondaries and whether to round-robin responses that include multiple A records. A name server is represented by an instance of the MicrosoftDNS_Server class. Table 14-1[2] contains all the property methods defined in the MicrosoftDNS_Server class.
The MicrosoftDNS_Server class also provides a few methods to initiate certain actions on the name server. Two of the most useful are StartService and StopService, which allow you to start and stop the DNS Server service. Table 14-2 lists MicrosoftDNS_Server methods.
14.3.1 Listing a Name Server's PropertiesThe first step to programmatically managing your name server's configuration is to see what settings you currently have in place and determine whether any need to be modified. With WMI, it's really easy to list all properties for a name server. The following example shows how to do it: strServer = "terminator.movie.edu"
' Instantiate a WMI object for the target server
set objDNS = GetObject("winmgmts:\\" & strServer & "\root\MicrosoftDNS")
' Get an instance of the MicrosoftDNS_Server class
set objDNSServer = objDNS.Get("MicrosoftDNS_Server.Name="".""")
' Iterate over each property using Properties_
Wscript.Echo objDNSServer.Properties_.Item("Name") & ":"
for each objProp in objDNSServer.Properties_
if IsNull(objProp.Value) then
Wscript.Echo " " & objProp.Name & " : NULL"
else
if objProp.IsArray = TRUE then
For I = LBound(objProp.Value) to UBound(objProp.Value)
wscript.echo " " & objProp.Name & " : " & objProp.Value(I)
next
else
wscript.echo " " & objProp.Name & " : " & objProp.Value
end if
end if
next
After getting a WMI object for the DNS Provider (root\MicrosoftDNS), we get a MicrosoftDNS_Server object by looking for the "." instance. Since there can be only one instance of MicrosoftDNS_Server running on any given computer, we do not need to worry about multiple objects. After getting a MicrosoftDNS_Server object, we iterate through all the properties of the object and print each one out. Note that we have added special checks for values that contain arrays in order to print each element of the array. In that case, we use Lbound and Ubound to iterate over all the values for the array. 14.3.2 Configuring a Name ServerNow that we can see what values have been set on our name server, we can change some of them. We simply need to set the property method (e.g., EventLogLevel) to the correct value. This example shows how to do it: strServer = "terminator.movie.edu"
on error resume next
set objDNS = GetObject("winMgmts:\\" & strServer & "\root\MicrosoftDNS")
set objDNSServer = objDNS.Get("MicrosoftDNS_Server.Name="".""")
Wscript.Echo objDNSServer.Name & ":"
' See Table 14-1 for an explanation of each of these settings
objDNSServer.EventLogLevel = 4
objDNSServer.LooseWildcarding = TRUE
objDNSServer.MaxCacheTTL = 900
objDNSServer.MaxNegativeCacheTTL = 60
objDNSServer.AllowUpdate = 3
objDNSServer.Put_
if Err then
Wscript.Echo " Error occurred: " & Err.Description
else
WScript.Echo " Change successful"
end if
Note that we had to call Put_ at the end. If we hadn't, none of the changes would have been committed. This is similar to ADSI's SetInfo method, which must be called after modifying an object's property cache to make the change actually take effect. 14.3.3 Restarting the DNS Server ServiceSome changes you make to a DNS Server require the service to be restarted for the changes to take effect. We can utilize the StopService and StartService methods as shown in the following example to do this: strServer = "terminator.movie.edu"
on error resume next
set objDNS = GetObject("winMgmts:\\" & strServer & "\root\MicrosoftDNS")
set objDNSServer = objDNS.Get("MicrosoftDNS_Server.Name="".""")
objDNSServer.StopService
if Err Then
WScript.Echo "StopService failed: " & Err.Description
Wscript.Quit
end if
objDNSServer.StartService
if Err Then
WScript.Echo "StartService failed: " & Err.Description
Wscript.Quit
end if
WScript.Echo "Restart successful"
14.3.4 Putting It Together: Configuration Check ScriptBuilding on the examples we've used so far in this chapter, we can now write a robust script to check name server configurations. Such a script can be very important, especially in large environments with many name servers. Unless you have a script that routinely checks the configuration on all of your name servers, it's very likely that those servers will not have an identical configuration. If they don't have identical configurations, then when problems pop up, you may end up spending a lot of time troubleshooting because of the discrepancies between the name servers. To perform the configuration checking, we store each setting in a VBScript Dictionary object. For those accustomed to other languages such as Perl, a Dictionary object is the VBScript analog to a hash or associative array. Another option would be to store the settings in a text file and read them into a Dictionary object when the script starts up. The following example shows the configuration check code: option explicit
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Dim arrServers
Dim strUsername, strPassword
Dim dicDNSConfig
' Array of DNS servers to check
arrServers = Array("terminator.movie.edu","fx.movie.edu")
' User and password that can modify the config on the DNS servers
strUsername = "dnsadmin"
strPassword = "dnspwd"
' This dictionary object will contain the key value pairs for all the settings
' that you want to check and configure on the DNS servers
Set dicDNSConfig = CreateObject("Scripting.Dictionary")
dicDNSConfig.Add "AllowUpdate", 1
dicDNSConfig.Add "LooseWildCarding", TRUE
dicDNSConfig.Add "MaxCacheTTL", 900
dicDNSConfig.Add "MaxNegativeCacheTTL", 60
dicDNSConfig.Add "EventLogLevel", 0
dicDNSConfig.Add "StrictFileParsing", TRUE
dicDNSConfig.Add "DisableAutoReverseZones", TRUE
Dim arrDNSConfigKeys
arrDNSConfigKeys = dicDNSConfig.keys
Dim objLocator
Set objLocator = CreateObject("WbemScripting.SWbemLocator")
Dim x, y, boolRestart
For x = LBound(arrServers) to UBound(arrServers)
boolRestart = False
WScript.echo arrServers(x)
Dim objDNS, objDNSServer
Set objDNS = objLocator.ConnectServer(arrServers(x), "root\MicrosoftDNS", _
strUserName, strPassword)
set objDNSServer = objDNS.Get("MicrosoftDNS_Server.Name="".""")
for y = 0 To dicDNSConfig.Count - 1
Dim strKey
strKey = arrDNSConfigKeys(y)
WScript.Echo " Checking " & strKey
if dicDNSConfig.Item(strKey) <> objDNSServer.Properties_.Item(strKey) then
objDNSServer.Properties_.Item(strKey).value = dicDNSConfig(strKey)
objDNSServer.Put_
boolRestart = TRUE
if Err Then
WScript.Echo " Error setting " & strKey & " : " & Err.Description
Wscript.Quit
else
WScript.Echo " " & strKey & " updated"
end if
end if
Next
if boolRestart then
objDNSServer.StopService
if Err Then
WScript.Echo "StopService failed: " & Err.Description
Wscript.Quit
end if
objDNSServer.StartService
if Err Then
WScript.Echo "StartService failed: " & Err.Description
Wscript.Quit
end if
WScript.Echo "Restarted"
end if
WScript.Echo ""
next
Besides the use of the Dictionary object, most of the script is a combination of the other three examples shown so far in this chapter. We added a server array so that you can check multiple servers at once. For each server, the script simply checks each key in the Dictionary object to see if its value matches the key on the name server. If not, it modifies the server and commits the change via Put_. After it's done looping through all the settings, it restarts the DNS Server service if a change has been made to its configuration. It then proceeds to the next server. One enhancement that would make the process even more automated would be to dynamically query the list of name servers instead of hard-coding them in an array. You would need to look up the NS records for one or more zones that your name servers are authoritative for. As long as an NS record is added for each new name server, the script would automatically discover new name servers on subsequent runs. Later in the chapter, we show how to query name servers with the DNS Provider. 14.3.5 Monitoring Server PerformanceIf you've ever wanted a programmatic way to access the output of the dnscmd /statistics command, now you have one. The MicrosoftDNS_Statistic class provides complete access to all the performance metrics you can get using dnscmd or Performance Monitor. And it's easy too! Check out this script, which prints out all of the statistics: strServer = "terminator.movie.edu "
set objDNS = GetObject("winMgmts:\\" & strServer & "\root\MicrosoftDNS")
set objDNSServer = objDNS.Get("MicrosoftDNS_Server.Name="".""")
set objStats = objDNS.ExecQuery("Select * from MicrosoftDNS_Statistic ")
for each objStat in objStats
WScript.Echo " " & objStat.Name & " : " & objStat.Value
next
And if you want to access only a subset of the metrics (for example, all of the entries that start with "Records") you only need to modify the WQL query slightly: set objStats = objDNS.ExecQuery("Select * from MicrosoftDNS_Statistic " & _
where Name like 'Records%' ")
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