This example uses the donationware component, ASPDNS (alternative) for IP lookups

Code:

if Request.QueryString("lookup") <> "" then
  dim objDNSLookup, sResult, sReversedIP, sLookupIP, nLastDotPosition, nNextDotBackPosition, nLoop

  sLookupIP = Request.QueryString("lookup")
  nLastDotPosition = len(sLookupIP)
  for nLoop = 0 to 3
   sLookupIP = Left(sLookupIP, nLastDotPosition)
   nNextDotBackPosition = instrrev(sLookupIP, ".")
   sReversedIP = sReversedIP & mid(sLookupIP,nNextDotBackPosition+1)&"."
   nLastDotPosition = nNextDotBackPosition-1
  next
  sLookupIP = sReversedIP & Request.QueryString("lookupSuffix")

  set objDNSLookup = Server.CreateObject("ASPDNSX.RealDNSLookup")
  objDNSLookup.DNSServer = Request.QueryString("xblServer")
  objDNSLookup.TimeOut = 10000
  
  sResult = objDNSLookup.GetIPFromName(trim(Request.QueryString("lookup")))
  if Len(sResult) = 0 then
    Response.Write "Forward DNS Resolution Failed. Error identified as " & objDNSLookup.LastError & "<br>"
  else
    Response.Write "The hostname " & Request.QueryString("lookup") & "resolves to ip address(es) " & Replace(sResult,vbcrlf,", ") & "<br>"
  end if
  
  set objDNSLookup = Nothing
end if
  

Now, to do something more fun, like redirect web hits from an RBLed server, we can have a custom global.asa

<SCRIPT LANGUAGE="VBScript" RUNAT="Server">
  Sub Session_OnStart
 dim objDNSLookup, sResult, sReversedIP, sLookupIP, nLastDotPosition, nNextDotBackPosition, nLoop

  sLookupIP = Request.ServerVariables("REMOTE_HOST")
  nLastDotPosition = len(sLookupIP)
  for nLoop = 0 to 3
   sLookupIP = Left(sLookupIP, nLastDotPosition)
   nNextDotBackPosition = instrrev(sLookupIP, ".")
   sReversedIP = sReversedIP & mid(sLookupIP,nNextDotBackPosition+1)&"."
   nLastDotPosition = nNextDotBackPosition-1
  next
  sLookupIP = sReversedIP & "spews.relay.osirusoft.com"

  set objDNSLookup = Server.CreateObject("ASPDNSX.RealDNSLookup")
  objDNSLookup.DNSServer = "216.102.236.44" ' Relay server. An IP address is quicker than a FQDN.
  objDNSLookup.TimeOut = 10000
  
  sResult = objDNSLookup.GetIPFromName(trim(Request.QueryString("lookup")))
  if Len(sResult) <> 0 then
    ' We have a resolved lookup, we could do a case here if we wanted.
    ' Instead I assume that any result is an xBLed host.
    Response.Redirect("http://www.spews.org")
  end if
  
  set objDNSLookup = Nothing
  End Sub

Because this is ASP, and not somthing more optimised like an ISAPI filter, this can kill your server. But it illustrates the idea.

[root]