What is the best way of validating an IP Address?

I have a method to validate a parameter IP Address. Being new to development as a whole I would like to know if there is a better way of doing this.

/// <summary>
/// Check IP Address, will accept 0.0.0.0 as a valid IP
/// </summary>
/// <param name="strIP"></param>
/// <returns></returns>
public bool CheckIPValid(string strIP)
{
    //  Split string by ".", check that array length is 3
    char chrFullStop = '.';
    string[] arrOctets = strIP.Split(chrFullStop);
    if (arrOctets.Length != 4)
    {
        return false;
    }
    //  Check each substring checking that the int value is less than 255 and that is char[] length is !> 2
    Int16 MAXVALUE = 255;
    Int32 temp; // Parse returns Int32
    foreach (string strOctet in arrOctets)
    {
        if (strOctet.Length > 3)
        {
            return false;
        }

        temp = int.Parse(strOctet);
        if (temp > MAXVALUE)
        {
            return false;
        }
    }
    return true;
}

Its simple (I could do it) but it seems to do the trick.

The limitation with IPAddress.TryParse method is that it verifies if a string could be converted to IP address, thus if it is supplied with a string value like "5", it consider it as "0.0.0.5".

Another approach to validate an IPv4 could be following :

public bool ValidateIPv4(string ipString)
{
    if (String.IsNullOrWhiteSpace(ipString))
    {
        return false;
    }

    string[] splitValues = ipString.Split('.');
    if (splitValues.Length != 4)
    {
        return false;
    }

    byte tempForParsing;

    return splitValues.All(r => byte.TryParse(r, out tempForParsing));
}

It could be tested like:

List<string> ipAddresses = new List<string>
{
    "2",
    "1.2.3",
    "1.2.3.4",
    "255.256.267.300",
    "127.0.0.1",
};
foreach (var ip in ipAddresses)
{
    Console.WriteLine($"{ip} ==> {ValidateIPv4(ip)}");
}

The output will be:

2 ==> False
1.2.3 ==> False
1.2.3.4 ==> True
255.256.267.300 ==> False
127.0.0.1 ==> True

You can also use IPAddress.TryParse but it has the limitations and could result in incorrect parsing.

System.Net.IPAddress.TryParse Method

> Note that TryParse returns true if it parsed the input successfully, > but that this does not necessarily mean that the resulting IP address > is a valid one. Do not use this method to validate IP addresses.

But this would work with normal string containing at least three dots. Something like:

string addrString = "192.168.0.1";
IPAddress address;
if (IPAddress.TryParse(addrString, out address)) {
       //Valid IP, with address containing the IP
} else {
       //Invalid IP
}

With IPAddress.TryParse you can check for existence of three dots and then call TryParse like:

public static bool ValidateIPv4(string ipString)
{
    if (ipString.Count(c => c == '.') != 3) return false;
    IPAddress address;
    return IPAddress.TryParse(ipString, out address);
}

using System.Net;
public static bool CheckIPValid(string strIP)
{
    IPAddress result = null;
    return
        !String.IsNullOrEmpty(strIP) &&
        IPAddress.TryParse(strIP, out result);
}

and you're done

Edit 1

Added some additional checks to prevent exceptions being thrown (which are costly). PS it won't handle unicode.

Edit 2

@StephenMurby IPAddress.TryParse will return true if it successfully parsed the string. If you check the [documentation][1] for the method though it will throw an exception in two cases.

1. The string is null.
2. The string contains unicode characters.

Its up to you to decide (design decision) whether you want to throw exceptions or return false. When it comes to parsing I generally prefer to return false rather than exceptions (the assumption being this is input that's not guaranteed to be correct).

Breaking the return statement down, I am saying,

1. The string is not null (nor empty which won't parse anyway) AND
2. The IP address parses correctly.

Remember C# boolean expressions are [lazy evaluated][2], so the CLR won't attempt to even parse the string if it is null or empty.

About the missing if, you can do something like,

if (IP.TryParse(strIP, out result)
{
    return true;
}

But all you really doing is saying if something is true, return true. Easier to just return the expression straight away. [1]: http://msdn.microsoft.com/en-us/library/system.net.ipaddress.tryparse [2]: http://en.wikipedia.org/wiki/Lazy_evaluation

The best Regex solution (useful for MVC DataAnnotations) :

^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$

C#

Regex.IsMatch(value, "^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$")

Without using IPAddress class and validating against byte, which is far better than the Int<256 approach.

    public Boolean CheckIPValid(String strIP)
    {
        //  Split string by ".", check that array length is 4
        string[] arrOctets = strIP.Split('.');
        if (arrOctets.Length != 4)
            return false;

        //Check each substring checking that parses to byte
        byte obyte = 0;
        foreach (string strOctet in arrOctets)
            if (!byte.TryParse(strOctet, out obyte)) 
                return false;

        return true;
    }

The framework provides the IPAddress class which in turn provides you the Parse and TryParse methods.

// myAddress is a System.Net.IPAddress instance
if (System.Net.IPAddress.TryParse(strIP , out myAddress)) 
    // IP is valid
else
    // IP isn't valid

Surprised no one offered a Regex solution. All you need is to include System.Text.RegularExpressions. For readability both in actual code and for this example, I ALWAYS chunk my regex pattern into a string array and then join it.

        // Any IP Address
        var Value = "192.168.0.55"; 
        var Pattern = new string[]
        {
            "^",                                            // Start of string
            @"([01]?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])\.",    // Between 000 and 255 and "."
            @"([01]?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])\.",
            @"([01]?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])\.",
            @"([01]?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])",      // Same as before, no period
            "$",                                            // End of string
        };

        // Evaluates to true 
        var Match = Regex.IsMatch(Value, string.Join(string.Empty, Pattern));

You can process like that it it is either an ipv4 or ipv6:

    public static string CheckIPValid(string strIP)
    {
        //IPAddress result = null;
        //return !String.IsNullOrEmpty(strIP) && IPAddress.TryParse(strIP, out result);
        IPAddress address;
        if (IPAddress.TryParse(strIP, out address))
        {
            switch (address.AddressFamily)
            {
                case System.Net.Sockets.AddressFamily.InterNetwork:
                    // we have IPv4
                    return "ipv4";
                //break;
                case System.Net.Sockets.AddressFamily.InterNetworkV6:
                    // we have IPv6
                    return "ipv6";
                //break;
                default:
                    // umm... yeah... I'm going to need to take your red packet and...
                    return null;
                    //break;
            }
        }
        return null;
    }

try with this:

private bool IsValidIP(String ip)
    {
        try
        {
            if (ip == null || ip.Length == 0)
            {
                return false;
            }

            String[] parts = ip.Split(new[] { "." }, StringSplitOptions.None);
            if (parts.Length != 4)
            {
                return false;
            }

            foreach (String s in parts)
            {
                int i = Int32.Parse(s);
                if ((i < 0) || (i > 255))
                {
                    return false;
                }
            }
            if (ip.EndsWith("."))
            {
                return false;
            }

            return true;
        }
        catch (Exception e)
        {
            return false;
        }
    }

If you want to just check if is valid do only:

bool isValid = IPAddress.TryParse(stringIP, out IPAddress _);

It will valid even if this is above 255 and if have dots, so no need to check it.

For validating IP Address, use below package

Packages:-

using System.Net;  //To use IPAddress, inbuilt functionality
using System.Net.Sockets; //To access AddressFamily,
using System.Text.RegularExpression; //For Regex.IsMatch()

Method:-

public bool ValidIPAddress(string IP)
{
    //Validate IP Address , neither IPV4, or V6

    if (IPAddress.TryParse(IP, out var address) == false)
       return false;
    //check for IPV6

    if (address.AddressFamily == AddressFamily.InterNetworkV6)

    {

        if (IP.IndexOf("::") > -1)

            return true;

        return false;

    }

    //check for IPV4

    else

    {

    //Ipv4 address shouldn't start with 0 eg..it is invalid 0XX.0XX.0XX.0XX
        if (Regex.IsMatch(IP, @"(^0\d|\.0\d)"))

            return false;

        else if (IP.Count(c => c == '.') != 3)

            return false;

        else

            return true;

    }

}

check on below link if needed:-

https://lncharan.blogspot.com/2020/09/validate-ip-address-in-c.html

There is an easy way to do this, but it requires internet connection to check the IP or host name:

using System;
using System.Net;

var dnsAddress = ///

try
{
    // IP like 8.8.8.8
    if (IPAddress.TryParse(dnsAddress, out var ipAddress)
        && Dns.GetHostAddresses(ipAddress.ToString()).Length >= 1)
    {
        return true;
    }

    // Hostname like smtp.gmail.com
    if (Dns.GetHostEntry(dnsAddress).AddressList.Length >= 1)
    {
        return true;
    }

    return false;
}
catch (Exception exception) when (
            exception is ArgumentNullException
            || exception is ArgumentOutOfRangeException
            || exception is System.Net.Sockets.SocketException
            || exception is ArgumentException
)
{
    // Write log message, if necessary

    return false;
}