When a IP-Range is written as aaa.bbb.ccc.ddd/netmask (CIDR Notation) I need to calculate the first and the last included ip address in this range with C#.
Example:
Input: 192.168.0.1/25
Result: 192.168.0.1 - 192.168.0.126
I would recommend the use of IPNetwork Library https://github.com/lduchosal/ipnetwork. As of version 2, it supports IPv4 and IPv6 as well.
IPv4
IPNetwork ipnetwork = IPNetwork.Parse("192.168.0.1/25");
Console.WriteLine("Network : {0}", ipnetwork.Network);
Console.WriteLine("Netmask : {0}", ipnetwork.Netmask);
Console.WriteLine("Broadcast : {0}", ipnetwork.Broadcast);
Console.WriteLine("FirstUsable : {0}", ipnetwork.FirstUsable);
Console.WriteLine("LastUsable : {0}", ipnetwork.LastUsable);
Console.WriteLine("Usable : {0}", ipnetwork.Usable);
Console.WriteLine("Cidr : {0}", ipnetwork.Cidr);
Output
Network : 192.168.0.0
Netmask : 255.255.255.128
Broadcast : 192.168.0.127
FirstUsable : 192.168.0.1
LastUsable : 192.168.0.126
Usable : 126
Cidr : 25
Have fun !
Invert mask (XOR with ones), AND it with IP. Add 1. This will be the starting range. OR IP with mask. This will be the ending range.
Input: 192.168.0.1/25
The mask is this part: /25
To find the network address do the following:
Subtract the mask from the ip length (32 - mask) = 32 - 25 = 7 and take those bits from the right
In the given ip address
I.e: 192.168.0.1
in binary is:
11111111 11111111 00000000 00000001
Now, taking 7 bits from right '0'
1111111 11111111 00000000 00000000
Which in decimal is:
192.168.0.0
(this is the network address)
To find first valid/usable ip address add +1 to network address I.e: 192.168.0.1
To find the last/broadcast address the procedure is same as that of finding network address but here you have to make (32-mask) bits from right to '1'
I.e: 11111111 11111111 00000000 01111111
Which in decimal is 192.168.0.127
To find the last valid/usable ip address subtract 1 from the broadcast address
I.e: 192.168.0.126
I'll just post the code:
IPAddress ip = new IPAddress(new byte[] { 192, 168, 0, 1 });
int bits = 25;
uint mask = ~(uint.MaxValue >> bits);
// Convert the IP address to bytes.
byte[] ipBytes = ip.GetAddressBytes();
// BitConverter gives bytes in opposite order to GetAddressBytes().
byte[] maskBytes = BitConverter.GetBytes(mask).Reverse().ToArray();
byte[] startIPBytes = new byte[ipBytes.Length];
byte[] endIPBytes = new byte[ipBytes.Length];
// Calculate the bytes of the start and end IP addresses.
for (int i = 0; i < ipBytes.Length; i++)
{
startIPBytes[i] = (byte)(ipBytes[i] & maskBytes[i]);
endIPBytes[i] = (byte)(ipBytes[i] | ~maskBytes[i]);
}
// Convert the bytes to IP addresses.
IPAddress startIP = new IPAddress(startIPBytes);
IPAddress endIP = new IPAddress(endIPBytes);
I know this is an older question, but I found this nifty library on nuget that seems to do just the trick for me:
You might already know this, but to check that you're getting this stuff right have a look at http://www.subnet-calculator.com/ - you can see there how the bits represent the network and host portions of the address.
I learned this shortcut from working at the network deployment position. It helped me so much, I figured I will share this secret with everyone. So far, I have not able to find an easier way online that I know of.
For example a network 192.115.103.64 /27, what is the range?
just remember that subnet mask is 0, 128, 192, 224, 240, 248, 252, 254, 255
255.255.255.255 11111111.11111111.11111111.11111111 /32
255.255.255.254 11111111.11111111.11111111.11111110 /31
255.255.255.252 11111111.11111111.11111111.11111100 /30
255.255.255.248 11111111.11111111.11111111.11111000 /29
255.255.255.240 11111111.11111111.11111111.11110000 /28
255.255.255.224 11111111.11111111.11111111.11100000 /27
255.255.255.192 11111111.11111111.11111111.11000000 /26
255.255.255.128 11111111.11111111.11111111.10000000 /25
255.255.255.0 11111111.11111111.11111111.00000000 /24
from /27 we know that (11111111.11111111.11111111.11100000). Counting from the left, it is the third number from the last octet, which equal 255.255.255.224 subnet mask. (Don't count 0, 0 is /24) so 128, 192, 224..etc
Here where the math comes in:
use the subnet mask - subnet mask of the previous listed subnet mask in this case 224-192=32
We know 192.115.103.64 is the network: 64 + 32 = 96 (the next network for /27)
which means we have .0 .32. 64. 96. 128. 160. 192. 224. (Can't use 256 because it is .255)
Here is the range 64 -- 96.
network is 64.
first host is 65.(first network +1)
Last host is 94. (broadcast -1)
broadcast is 95. (last network -1)
Source: Stackoverflow.com