Using code to implement access restrictions on IP

This is previously written in ASP, I would like to change into asp.net to everyone, and then think we can read the algorithm on the line.
The key of IP alignment is the linearization of IP address
<%
' Access to IP
' 218.7.44.0-218.7.45.253
' 61.180.240.0-61.180.240.253
' 202.118.208.0-202.118.223.253
'
' 218.7.44.0 3657903103
' 218.7.45.253 3657903612
'
' 61.180.240.0 1035268095
' 61.180.240.253 1035268348
'
' 202.118.208.0 3396784127
' 202.118.223.253 3396788220
Ip=request.servervariables ("REMOTE_ADDR")
Sip=split (IP, ".")
Num=cint (SIP (0)) *256*256*256+cint (SIP (1)) *256*256+cint (SIP (2)) *256+cint (SIP (3))-1
Response.Write (IP)
Response.Write ("<br>")
if (num>=3657903103 and num<=3657903612) or (num>=1035268095 and num<=1035268348) or (num>=3396784127 and num<=3396788220)) then
Response.Write ("Sorry, your IP is not legal!") ")
Response. End ()
Else
Response.Write ("Your IP is legitimate")
End If
%>