/*
C# Network Programming
by Richard Blum
Publisher: Sybex
ISBN: 0782141765
*/
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
public class FindMask
{
public static void Main()
{
byte[] data = new byte[1024];
int recv;
Socket host = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp);
IPEndPoint iep = new IPEndPoint(IPAddress.Broadcast, 0);
EndPoint ep = (EndPoint)iep;
ICMP packet = new ICMP();
packet.Type = 0x11;
packet.Code = 0x00;
packet.Checksum = 0;
Buffer.BlockCopy(BitConverter.GetBytes(1), 0, packet.Message, 0, 2);
Buffer.BlockCopy(BitConverter.GetBytes(1), 0, packet.Message, 2, 2);
Buffer.BlockCopy(BitConverter.GetBytes(0), 0, packet.Message, 4, 4);
packet.MessageSize = 8;
int packetsize = packet.MessageSize + 4;
UInt16 chksm = packet.getChecksum();
packet.Checksum = chksm;
host.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 3000);
host.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Broadcast, 1);
host.SendTo(packet.getBytes(), packetsize, SocketFlags.None, iep);
try
{
data = new byte[1024];
recv = host.ReceiveFrom(data, ref ep);
} catch (SocketException)
{
Console.WriteLine("Unable to determine subnet mask for this subnet");
return;
}
ICMP response = new ICMP(data, recv);
Console.WriteLine("Received ICMP Type {0} packet", response.Type);
long answer = BitConverter.ToUInt32(response.Message, 4);
IPAddress netmask = new IPAddress(answer);
Console.WriteLine("The subnet mask for this subnet is: {0}", netmask.ToString());
}
}
class ICMP
{
public byte Type;
public byte Code;
public UInt16 Checksum;
public int MessageSize;
public byte[] Message = new byte[1024];
public ICMP()
{
}
public ICMP(byte[] data, int size)
{
Type = data[20];
Code = data[21];
Checksum = BitConverter.ToUInt16(data, 22);
MessageSize = size - 24;
Buffer.BlockCopy(data, 24, Message, 0, MessageSize);
}
public byte[] getBytes()
{
byte[] data = new byte[MessageSize + 9];
Buffer.BlockCopy(BitConverter.GetBytes(Type), 0, data, 0, 1);
Buffer.BlockCopy(BitConverter.GetBytes(Code), 0, data, 1, 1);
Buffer.BlockCopy(BitConverter.GetBytes(Checksum), 0, data, 2, 2);
Buffer.BlockCopy(Message, 0, data, 4, MessageSize);
return data;
}
public UInt16 getChecksum()
{
UInt32 chcksm = 0;
byte[] data = getBytes();
int packetsize = MessageSize + 8;
int index = 0;
while ( index < packetsize)
{
chcksm += Convert.ToUInt32(BitConverter.ToUInt16(data, index));
index += 2;
}
chcksm = (chcksm >> 16) + (chcksm & 0xffff);
chcksm += (chcksm >> 16);
return (UInt16)(~chcksm);
}
}
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