/**
C# Network Programming 
by Richard Blum
Publisher: Sybex 
ISBN: 0782141765
*/
using System;
using System.Text;
using System.Net;
using System.Net.Sockets;
public class SimpleSNMP
{
  public static void Main(string[] argv)
  {
   int commlength, miblength, datatype, datalength, datastart;
   int uptime = 0;
   string output;
   SNMP conn = new SNMP();
   byte[] response = new byte[1024];
   Console.WriteLine("Device SNMP information:");
   // Send sysName SNMP request
   response = conn.get("get", argv[0], argv[1], "1.3.6.1.2.1.1.5.0");
   if (response[0] == 0xff)
   {
     Console.WriteLine("No response from {0}", argv[0]);
     return;
   }
   // If response, get the community name and MIB lengths
   commlength = Convert.ToInt16(response[6]);
   miblength = Convert.ToInt16(response[23 + commlength]);
   // Extract the MIB data from the SNMP response
   datatype = Convert.ToInt16(response[24 + commlength + miblength]);
   datalength = Convert.ToInt16(response[25 + commlength + miblength]);
   datastart = 26 + commlength + miblength;
   output = Encoding.ASCII.GetString(response, datastart, datalength);
   Console.WriteLine(" sysName - Datatype: {0}, Value: {1}",
       datatype, output);
   // Send a sysLocation SNMP request
   response = conn.get("get", argv[0], argv[1], "1.3.6.1.2.1.1.6.0");
   if (response[0] == 0xff)
   {
     Console.WriteLine("No response from {0}", argv[0]);
     return;
   }
   // If response, get the community name and MIB lengths
   commlength = Convert.ToInt16(response[6]);
   miblength = Convert.ToInt16(response[23 + commlength]);
   // Extract the MIB data from the SNMP response
   datatype = Convert.ToInt16(response[24 + commlength + miblength]);
   datalength = Convert.ToInt16(response[25 + commlength + miblength]);
   datastart = 26 + commlength + miblength;
   output = Encoding.ASCII.GetString(response, datastart, datalength);
   Console.WriteLine(" sysLocation - Datatype: {0}, Value: {1}", datatype, output);
   // Send a sysContact SNMP request
   response = conn.get("get", argv[0], argv[1], "1.3.6.1.2.1.1.4.0");
   if (response[0] == 0xff)
   {
     Console.WriteLine("No response from {0}", argv[0]);
     return;
   }
   // Get the community and MIB lengths
   commlength = Convert.ToInt16(response[6]);
   miblength = Convert.ToInt16(response[23 + commlength]);
   // Extract the MIB data from the SNMP response
   datatype = Convert.ToInt16(response[24 + commlength + miblength]);
   datalength = Convert.ToInt16(response[25 + commlength + miblength]);
   datastart = 26 + commlength + miblength;
   output = Encoding.ASCII.GetString(response, datastart, datalength);
   Console.WriteLine(" sysContact - Datatype: {0}, Value: {1}",
       datatype, output);
   // Send a SysUptime SNMP request
   response = conn.get("get", argv[0], argv[1], "1.3.6.1.2.1.1.3.0");
   if (response[0] == 0xff)
   {
     Console.WriteLine("No response from {0}", argv[0]);
     return;
   }
   // Get the community and MIB lengths of the response
   commlength = Convert.ToInt16(response[6]);
   miblength = Convert.ToInt16(response[23 + commlength]);
   // Extract the MIB data from the SNMp response
   datatype = Convert.ToInt16(response[24 + commlength + miblength]);
   datalength = Convert.ToInt16(response[25 + commlength + miblength]);
   datastart = 26 + commlength + miblength;
   // The sysUptime value may by a multi-byte integer
   // Each byte read must be shifted to the higher byte order
   while(datalength > 0)
   {
     uptime = (uptime << 8) + response[datastart++];
     datalength--;
   }
   Console.WriteLine(" sysUptime - Datatype: {0}, Value: {1}",
       datatype, uptime);
  }
}
class SNMP
{
  public SNMP()
  {
  }
  public byte[] get(string request, string host, string community, string mibstring)
  {
   byte[] packet = new byte[1024];
   byte[] mib = new byte[1024];
   int snmplen;
   int comlen = community.Length;
   string[] mibvals = mibstring.Split('.');
   int miblen = mibvals.Length;
   int cnt = 0, temp, i;
   int orgmiblen = miblen;
   int pos = 0;
   // Convert the string MIB into a byte array of integer values
   // Unfortunately, values over 128 require multiple bytes
   // which also increases the MIB length
   for (i = 0; i < orgmiblen; i++)
   {
     temp = Convert.ToInt16(mibvals[i]);
     if (temp > 127)
     {
      mib[cnt] = Convert.ToByte(128 + (temp / 128));
      mib[cnt + 1] = Convert.ToByte(temp - ((temp / 128) * 128));
      cnt += 2;
      miblen++;
     } else
     {
      mib[cnt] = Convert.ToByte(temp);
      cnt++;
     }
   }
   snmplen = 29 + comlen + miblen - 1; //Length of entire SNMP packet
   //The SNMP sequence start
   packet[pos++] = 0x30; //Sequence start
   packet[pos++] = Convert.ToByte(snmplen - 2); //sequence size
   //SNMP version
   packet[pos++] = 0x02; //Integer type
   packet[pos++] = 0x01; //length
   packet[pos++] = 0x00; //SNMP version 1
   //Community name
   packet[pos++] = 0x04; // String type
   packet[pos++] = Convert.ToByte(comlen); //length
   //Convert community name to byte array
   byte[] data = Encoding.ASCII.GetBytes(community);
   for (i = 0; i < data.Length; i++)
   {
     packet[pos++] = data[i];
   }
   //Add GetRequest or GetNextRequest value
   if (request == "get")
     packet[pos++] = 0xA0;
   else
     packet[pos++] = 0xA1;
   packet[pos++] = Convert.ToByte(20 + miblen - 1); //Size of total MIB
   //Request ID
   packet[pos++] = 0x02; //Integer type
   packet[pos++] = 0x04; //length
   packet[pos++] = 0x00; //SNMP request ID
   packet[pos++] = 0x00;
   packet[pos++] = 0x00;
   packet[pos++] = 0x01;
   //Error status
   packet[pos++] = 0x02; //Integer type
   packet[pos++] = 0x01; //length
   packet[pos++] = 0x00; //SNMP error status
   //Error index
   packet[pos++] = 0x02; //Integer type
   packet[pos++] = 0x01; //length
   packet[pos++] = 0x00; //SNMP error index
   //Start of variable bindings
   packet[pos++] = 0x30; //Start of variable bindings sequence
   packet[pos++] = Convert.ToByte(6 + miblen - 1); // Size of variable binding
   packet[pos++] = 0x30; //Start of first variable bindings sequence
   packet[pos++] = Convert.ToByte(6 + miblen - 1 - 2); // size
   packet[pos++] = 0x06; //Object type
   packet[pos++] = Convert.ToByte(miblen - 1); //length
   //Start of MIB
   packet[pos++] = 0x2b;
   //Place MIB array in packet
   for(i = 2; i < miblen; i++)
     packet[pos++] = Convert.ToByte(mib[i]);
   packet[pos++] = 0x05; //Null object value
   packet[pos++] = 0x00; //Null
   //Send packet to destination
   Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram,
            ProtocolType.Udp);
   sock.SetSocketOption(SocketOptionLevel.Socket,
           SocketOptionName.ReceiveTimeout, 5000);
   IPHostEntry ihe = Dns.Resolve(host);
   IPEndPoint iep = new IPEndPoint(ihe.AddressList[0], 161);
   EndPoint ep = (EndPoint)iep;
   sock.SendTo(packet, snmplen, SocketFlags.None, iep);
   //Receive response from packet
   try
   {
     int recv = sock.ReceiveFrom(packet, ref ep);
   } catch (SocketException)
   {
     packet[0] = 0xff;
   }
   return packet;
  }
  public string getnextMIB(byte[] mibin)
  {
   string output = "1.3";
   int commlength = mibin[6];
   int mibstart = 6 + commlength + 17; //find the start of the mib section
   //The MIB length is the length defined in the SNMP packet
   // minus 1 to remove the ending .0, which is not used
   int miblength = mibin[mibstart] - 1;
   mibstart += 2; //skip over the length and 0x2b values
   int mibvalue;
   for(int i = mibstart; i < mibstart + miblength; i++)
   {
     mibvalue = Convert.ToInt16(mibin[i]);
     if (mibvalue > 128)
     {
      mibvalue = (mibvalue/128)*128 + Convert.ToInt16(mibin[i+1]);
      //ERROR here, it should be mibvalue = (mibvalue-128)*128 + Convert.ToInt16(mibin[i+1]);
      //for mib values greater than 128, the math is not adding up correctly  
      i++;
     }
     output += "." + mibvalue;
   }
   return output;
  }
}