How to check a input IP fall in a specific IP range

You might want to consider this library by @jsakamoto, which allows you to parse range of IP address strings such as "192.168.0.0/24" and "192.168.0.0/255.255.255.0" and "192.168.0.0-192.168.0.255", and can contains check. This library supports both IPv4 and IPv6.

https://github.com/jsakamoto/ipaddressrange

It can also be installed via NuGet:

http://www.nuget.org/packages/IPAddressRange/

using NetTools;
...
// rangeA.Begin is "192.168.0.0", and rangeA.End is "192.168.0.255".
var rangeA = IPAddressRange.Parse("192.168.0.0/255.255.255.0");
rangeA.Contains(IPAddress.Parse("192.168.0.34")); // is True.
rangeA.Contains(IPAddress.Parse("192.168.10.1")); // is False.
rangeA.ToCidrString(); // is 192.168.0.0/24

// rangeB.Begin is "192.168.0.10", and rangeB.End is "192.168.10.20".
var rangeB1 = IPAddressRange.Parse("192.168.0.10 - 192.168.10.20");
rangeB1.Contains(IPAddress.Parse("192.168.3.45")); // is True.
rangeB1.Contains(IPAddress.Parse("192.168.0.9")); // is False.

// Support shortcut range description. 
// ("192.168.10.10-20" means range of begin:192.168.10.10 to end:192.168.10.20.)
var rangeB2 = IPAddressRange.Parse("192.168.10.10-20");

// Support CIDR expression and IPv6.
var rangeC = IPAddressRange.Parse("fe80::/10"); 
rangeC.Contains(IPAddress.Parse("fe80::d503:4ee:3882:c586%3")); // is True.
rangeC.Contains(IPAddress.Parse("::1")); // is False.

public static bool IsInRange(string startIpAddr, string endIpAddr, string address)
{
    long ipStart = BitConverter.ToInt32(IPAddress.Parse(startIpAddr).GetAddressBytes().Reverse().ToArray(), 0);

    long ipEnd = BitConverter.ToInt32(IPAddress.Parse(endIpAddr).GetAddressBytes().Reverse().ToArray(), 0);

    long ip = BitConverter.ToInt32(IPAddress.Parse(address).GetAddressBytes().Reverse().ToArray(), 0);

    return ip >= ipStart && ip <= ipEnd; //edited
}

Console.WriteLine(IsInRange("100.0.0.1", "110.0.0.255", "102.0.0.4"));//true

There's nothing built into the framework, but it wouldn't take much effort to create an IPAddressRange class.

You'd compare the ranges by calling IPAddress.GetAddressBytes on the lower address, upper address and comparison address. Starting at the first byte, check if the comparison address is in the range of the upper/lower address.

This method works for both IPv4 and IPv6 addresses.

public class IPAddressRange
{
    readonly AddressFamily addressFamily;
    readonly byte[] lowerBytes;
    readonly byte[] upperBytes;

    public IPAddressRange(IPAddress lowerInclusive, IPAddress upperInclusive)
    {
        // Assert that lower.AddressFamily == upper.AddressFamily

        this.addressFamily = lowerInclusive.AddressFamily;
        this.lowerBytes = lowerInclusive.GetAddressBytes();
        this.upperBytes = upperInclusive.GetAddressBytes();
    }

    public bool IsInRange(IPAddress address)
    {
        if (address.AddressFamily != addressFamily)
        {
            return false;
        }

        byte[] addressBytes = address.GetAddressBytes();

        bool lowerBoundary = true, upperBoundary = true;

        for (int i = 0; i < this.lowerBytes.Length && 
            (lowerBoundary || upperBoundary); i++)
        {
            if ((lowerBoundary && addressBytes[i] < lowerBytes[i]) ||
                (upperBoundary && addressBytes[i] > upperBytes[i]))
            {
                return false;
            }

            lowerBoundary &= (addressBytes[i] == lowerBytes[i]);
            upperBoundary &= (addressBytes[i] == upperBytes[i]);
        }

        return true;
    }
}

NB: The above code could be extended to add public static factory methods FromCidr(IPAddress address, int bits)