SNMP C# in ASP.NET

SNMP (Simple Network Management Protocol). This simple yet powerful protocol allows you to query various  OIDs (Object Identifiers) associated with a particular device. You can find out different data about a device, and this code returns the value taking an input of OID, Host, and community string. The first portion is the SNMP class and then following that is the method I used. Both are included in my MobileExec program.

using System.Net.Sockets;


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;
    }
}


public void SNMPConnectOID(string arg0, string arg1, string OID)
    {
        Label1.ForeColor = Color.Black;
        Label1.Text = "Sorry! Software could not be found!";


        this.Label1.Style["text-align"] = "left";


        int commlength, miblength, datatype, datalength, datastart;
        
        string output;
        SNMP conn = new SNMP();
        byte[] response = new byte[1024];


        Label1.Text = "Device <b>" + arg0 + "</b> SNMP information, OID:<b>" + OID + "</b>:<br />";
        Label1.Text += "----------------------------------------------<br />";


        // Send sysName SNMP request
        response = conn.get("get", arg0, arg1, OID);
        if (response[0] == 0xff)
        {
            Label1.Text += "No response from " + arg0 + "<br />";
            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}" + "<br />",
                datatype, output);
        Label1.Text += "<b>"+ OID +"</b>- type: " + datatype + ", Value: " + output + "<br />";
        
    }