IPAddress.IsLoopback Method (IPAddress)


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Indicates whether the specified IP address is the loopback address.

Namespace:   System.Net
Assembly:  System (in System.dll)

Public Shared Function IsLoopback (
	address As IPAddress
) As Boolean


Type: System.Net.IPAddress

An IP address.

Return Value

Type: System.Boolean

true if address is the loopback address; otherwise, false.

The IsLoopback method compares address to Loopback and returns true if the two IP addresses are the same.

In the case of IPv4, that the IsLoopback method returns true for any IP address of the form 127.X.Y.Z (where X, Y, and Z are in the range 0-255), not just Loopback (

The following code example uses the IsLoopback method to determine whether the specified address is a loopback address.

Imports System
Imports System.Net
Imports System.Net.Sockets


Class IsLoopbackTest

   'Entry point which delegates to C-style main Private Function
   Public Overloads Shared Sub Main()
   End Sub

   Overloads Private Shared Sub Main(args() As String)

       If args.Length = 1 Then
         ' No parameters entered. Display program usage.
         Console.WriteLine("Please enter an IP address.")
         Console.WriteLine("Usage:   >ipaddress_isloopback any IPv4 or IPv6 address.")
         Console.WriteLine("Example: >ipaddress_isloopback")
         Console.WriteLine("Example: >ipaddress_isloopback 0:0:0:0:0:0:0:1")
      ' Parse the address string entered by the user.
      End If 
   End Sub 'Main

   ' This method calls the IPAddress.Parse method to check whether the 
   ' passed ipAddress parameter is in the correct format.
   ' Then it checks whether it represents a loopback address.
   ' Finally, it displays the results.
   Private Shared Sub parse(ipAdd As String)
      Dim loopBack As String = " is not a loopback address."

         ' Perform syntax check by parsing the address string entered by the user.
         Dim address As IPAddress = IPAddress.Parse(ipAdd)

         ' Perform semantic check by verifying that the address is a valid IPv4 
         ' or IPv6 loopback address. 
         If IPAddress.IsLoopback(address) And address.AddressFamily = AddressFamily.InterNetworkV6 Then
            loopBack = " is an IPv6 loopback address " + "whose internal format is: " + address.ToString() + "."
            If IPAddress.IsLoopback(address) And address.AddressFamily = AddressFamily.InterNetwork Then
               loopBack = " is an IPv4 loopback address " + "whose internal format is: " + address.ToString() + "."
            End If
         End If 
         ' Display the results.
         Console.WriteLine(("Your input address: " + """" + ipAdd + """" + loopBack))

      Catch e As FormatException
         Console.WriteLine("FormatException caught!!!")
         Console.WriteLine(("Source : " + e.Source))
         Console.WriteLine(("Message : " + e.Message))

      Catch e As Exception
         Console.WriteLine("Exception caught!!!")
         Console.WriteLine(("Source : " + e.Source))
         Console.WriteLine(("Message : " + e.Message))
      End Try
   End Sub 'parse 
End Class 'IsLoopbackTest

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Available since 2.0
Windows Phone Silverlight
Available since 7.1
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