CODEWITHSUNDEEP
sharp-snmp
Brian Mitchell
Brian Mitchell

Reputation: 929

Properly parse MAC Address

When I use tools such as snmp-walk or snmp-get to query an OID with a return type of MacAddress, It'll always parse the data as a HexString and display it properly. Even when they don't have the MIBs loaded it'll still works.

bash#snmpwalk -v 2c -c public 10.1.2.3 1.3.6.1.4.1.14179.2.2.1.1
    SNMPv2-SMI::enterprises.14179.2.2.1.1.1.16.189.24.206.212.64 = Hex-STRING: 10 BD 18 CE D4 40 
    SNMPv2-SMI::enterprises.14179.2.2.1.1.1.100.233.80.151.114.192 = Hex-STRING: 64 E9 50 97 72 C0

However, I can't seem to get the same result from Lextm.SharpSnmpLib (11.2.0). Data types of MacAddress don't get decoded correctly and it's a manual process to convert it to a proper MAC. 

public void WalkTable()
    {
    const string baseOid = "1.3.6.1.4.1.14179.2.2.1.1"; //The entire table
    const string community = "public";

    var ep = new IPEndPoint(IPAddress.Parse("10.1.2.3"), 161);
    var results = new List<Variable>();
    Messenger.Walk(VersionCode.V2, ep, new OctetString(community), new ObjectIdentifier(baseOid), results, 60000, WalkMode.WithinSubtree);

    foreach(var v in results)
    Console.WriteLine(v.Data.ToString());
    }

Incorrect Results

Am I doing something wrong or is this just how the library works?

Upvotes: 2

Views: 1626

Answers (1)

bbailes
bbailes

Reputation: 371

You are outputting the MAC Address as ASCII instead of Hex. Here's a quick method I put together that will detect non-ascii characters and output as hex if any are found.

public void WalkTable()
    {
    const string baseOid = "1.3.6.1.4.1.14179.2.2.1.1"; //The entire table
    const string community = "public";

    var ep = new IPEndPoint(IPAddress.Parse("10.1.2.3"), 161);
    var results = new List<Variable>();
    Messenger.Walk(VersionCode.V2, ep, new OctetString(community), new ObjectIdentifier(baseOid), results, 60000, WalkMode.WithinSubtree);

    foreach(var v in results)
        //If the result is an OctetString, check for ascii, otherwise use ToString()
        Console.WriteLine(v.Data.TypeCode.ToString()=="OctetString" ? DecodeOctetString(v.Data.ToBytes()) : v.Data.ToString())
    }
}

public string DecodeOctetString(byte[] raw)
{
    //First 2 bytes are the Type, so remove them
    byte[] bytes = new byte[raw.Length - 2];
    Array.Copy(raw, 2, bytes, 0, bytes.Length);

    //Check if there are any non-ascii characters
    bool ascii = true;
    foreach (char c in Encoding.UTF8.GetString(bytes))
    {
        if (c >= 128)
        {
            ascii = false;
        }
    }

    //If it's all ascii, return as ascii, else convert to hex
    return ascii ? Encoding.ASCII.GetString(bytes) : BitConverter.ToString(bytes);
}

Upvotes: 2

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