NOTE: On some systems the snmpd is running as its own user, which means it can't read /sys/devices/virtual/dmi/id/product_serial which is mode 0400. One solution is to include @reboot chmod 444 /sys/devices/virtual/dmi/id/product_serial in the crontab for root or equivalent.
Snmpc 7 serial number
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Non-x86 or SMBIOS-based systems, such as ARM-based Raspberry Pi units should query device tree locations for this metadata, for example: extend hardware '/bin/cat /sys/firmware/devicetree/base/model'extend serial '/bin/cat /sys/firmware/devicetree/base/serial-number'
SNMP agents store information in a Structure of Management Information (SMI), which is a hierarchical database that is similar to the directory structure in a filesystem. The individual files that store the information are called Management Information Bases (MIBs). Each MIB contains nodes of information that are stored in a tree structure. The tree contains branches, which move down from a root node. The branches are similar to the directory names in a directory path. Each branch eventually ends in a leaf, similar to a filename in a filesystem, that contains a specific piece of information about the SNMP agent. Each branching point in the tree corresponds to a MIB object and is identified by a number and a text string. The series of numbers that uniquely identifies a node or a leaf is called the Object Identifier (OID). As examples, OID .1.3.6.1.2.1.1.4 corresponds to sysContact (system contact information) in the standard MIB-II MIB, and OID .1.3.1.4.1.2636 corresponds to juniperMIB, which is the top node of the Juniper enterprise-specific portion of the MIB tree. Both these OIDs are absolute references because they start at the root node, which is indicated by the dot (.) before the first number (.1.3.1.4.1.2636 rather than 1.3.1.4.1.2636). In NMS and JUNOS software, you can refer to the OIDs by absolute OID or by name; the names are generally easier to remember and type. Figure 4-1 illustrates a portion of the MIB tree that leads to these OIDs and shows that each node has both text and a number to identify it.
MIBs are defined using a language called Abstract Syntax Notation 1 ( ASN.1). The IETF has defined a number of MIBs in various RFCs that contain objects common across all network devices. Some of these MIBs are mandatory, while others are optional. On NMS systems, most of the mandatory MIBs are typically compiled into the SNMP manager software. If you need standard MIBs that are not provided with your NMS, you can find them in the IETF RFCs and at other web sites, including -snmp.org, -editor.org, and -snmp.sourceforge.net. There is a list of SMI numbers on the IANA web site ( ).
The output shows the number and types of packets the router has received from and sent to the NMS. If you see any bad (invalid) community names, or if the number of names increases, this can indicate that one or more community names are configured incorrectly, or that an unauthorized manager, possibly a malicious user, is trying to access the agent.
Finally, choose a number to identify the alarm and to link the alarm with the event. Specify the number in the rising-alarm-index statement when monitoring a rising threshold or in the falling-alarm-index statement when monitoring a falling threshold. For alarm 1, rising-alarm-index 1 associates event 1 with this alarm.
Although some RS-232 connectors still cling desperately to audio hardware products around the world, for years Ethernet and the Internet Protocol (IP) have been replacing older serial communication formats as the connection of choice for monitoring and controlling audio as well as video, networking, and industrial equipment. Since the childhood of computer networking, network designers envisioned a world where a person's audio system, video system, HVAC system, and toaster all connect to the same network. To that end, computer scientists developed a protocol capable of managing any network device. The result was SNMP, which stands for Simple Network Management Protocol. SNMP was introduced in 1988 and now includes three distinct versions SNMPv1, SNMPv2, and SNMPv3. Due to the maturity of SNMP, many device manufacturers include support for this protocol in their products, and many SNMP management solutions exist off-the-shelf for common operating systems and programming languages. However, SNMP management capabilities are still lacking for today's control system platforms, requiring control system programmers to write their own SNMP management code.
The main purpose of an SNMP message is to control (set) or monitor (get) parameters on an SNMP agent. In SNMP, a parameter is an instance of a more generic object. For example, an SNMP agent may have several instances of a microphoneMute object -- one instance for each microphone input. An SNMP manager can set or get the value for each instance (each parameter). In an SNMP agent, parameters are arranged in a tree. SNMP uses an Object Identifier (OID) to specify the exact parameter to set or get in the tree. An OID is a list of numbers separated by periods. For example, the OID addressing the microphoneMute parameter in a Rane NM 1 is '1.3.6.1.4.1.2680.1.2.7.3.2.0'. This OID is actually a combination of two values. The first value is the OID of the generic object '1.3.6.1.4.1.2680.1.2.7.3.2'. The second is the instance value, which specifies the particular instance of the mirophoneMute object. The instance value in this case is 0, because the NM 1 has only one microphone input. But where do these OIDs come from?
Follow the Basic Encoding Rules when laying out the bytes of an SNMP message. The most fundamental rule states that each field is encoded in three parts: Type, Length, and Data. Type specifies the data type of the field using a single byte identifier. For a brief table of some data types and their identifiers, see Table 1. Length specifies the length in bytes of the following Data section, and Data is the actual value communicated (the number, string, OID, etc). One way to visualize encoding a field is shown in Figure 1.
There are two more Basic Encoding Rules necessary for encoding an SNMP message. Both apply to encoding OIDs. The first rule applies when encoding the first two numbers in the OID. According to BER, the first two numbers of any OID (x.y) are encoded as one value using the formula (40*x)+y. The first two numbers in an SNMP OID are always 1.3. Therefore, the first two numbers of an SNMP OID are encoded as 43 or 0x2B, because (40*1)+3 = 43. After the first two numbers are encoded, the subsequent numbers in the OID are each encoded as a byte. However, a special rule is required for large numbers because one byte (eight bits) can only represent a number from 0-255. For example, the number 2680 in the Rane NM 1 microphoneMute OID '1.3.6.1.4.1.2680.1.2.7.3.2.0' cannot be encoded using a single byte. The rule for large numbers states that only the lower 7 bits in the byte are used for holding the value (0-127). The highest order bit is used as a flag to let the recipient know that this number spans more than one byte. Therefore, any number over 127 must be encoded using more than one byte. According to this rule, the number 2680 must be encoded 0x94 0x78. Since the most significant bit is set in the first byte (0x94), the recipient knows to use the lower 7 bits from each byte (0x14 and 0x78) and decode the two bytes as (0x14 *128) + 0x78 = 2680.
To all the readers joining us at this point, because they are in a hurry, or because they enjoy reading the last chapter of their mystery novels first, welcome. Now is the time to create the SNMP message by applying the Basic Encoding Rules to the fields and laying out the bytes in the correct order. As an example, Figure 3 shows an SNMP GetRequest packet for the microphoneMute parameter on a Rane NM 1 (OID: 1.3.6.1.4.1.2680.1.2.7.3.2.0). It is important to remember that changing the number of bytes of any field in the SNMP message requires changing the Length byte of all the outer layers that enclose the edited field. For example, changing the GetRequest below to a SetRequest that sets the microphoneMute to a Value of 1 (0x01) requires changing the PDU data type to SetRequest (0xA3) and the Value field to an integer (0x04) of length 0x01 and data 0x01. However, increasing the length of the Value field also increases the length of the Varbind, Varbind List, PDU, and SNMP message fields.
The total number of octets received on the interface, including framing characters. This object is a 64-bit version of ifInOctets. Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime.
The total number of octets transmitted out of the interface, including framing characters. This object is a 64-bit version of ifOutOctets.Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime.
For packet-oriented interfaces, the number of inbound packets that contained errors preventing them from being deliverable to a higher-layer protocol. For character-oriented or fixed-length interfaces, the number of inbound transmission units that contained errors preventing them from being deliverable to a higher-layer protocol. Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime.
For packet-oriented interfaces, the number of outbound packets that contained errors preventing them from being deliverable to a higher-layer protocol. For character-oriented or fixed-length interfaces, the number of outbound transmission units that contained errors preventing them from being deliverable to a higher-layer protocol. Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime. 2ff7e9595c
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