For Each doppeltes In From x In Liste1 Where (From y In Liste2 Select _
  y.IP).Contains(x.IP) Select x
   Console.WriteLine(doppeltes.IP)
Next

For Each doppeltes In Liste1.Where(Function(x) Liste2.Select(Function(y) _
  y.IP).Contains(x.IP))
   Console.WriteLine(doppeltes.IP)
Next

For Each d In Liste1.Intersect(Liste2, New IPComparer)
   Console.WriteLine(d.IP)
Next
 
Class IPComparer
     Implements IEqualityComparer(Of DNS)
 
     Public Function Equals1(ByVal x As DNS, ByVal y As DNS) As Boolean _
       Implements System.Collections.Generic.IEqualityComparer(Of DNS).Equals
          If x.IP = y.IP Then Return True
          Return False
     End Function
 
     Public Function GetHashCode1(ByVal obj As DNS) As Integer Implements _
       System.Collections.Generic.IEqualityComparer(Of DNS).GetHashCode
          Return Nothing
     End Function
End Class