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SNMP protocol

Supported device types and versions
Communication line configuration
Communication station configuration
I/O tags configuration
Messages of Trap type receiving and processing
Browsing and reading the tree of values from the script
Literature
Changes and modifications
Document revisions

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Supported device types and versions

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Protocol SNMP protocol (Simple Network Management Protocol) is used for monitoring and administration of network components. It allows the detection of the network devices' status and the changing of their settings. In an application, it is possible to monitor the functionality of e.g., routers, switches, computers, etc.

To create a station equipped with the SNMP protocol, it is necessary to have a UDP line (line of of TCP/IP-UDP type). It is worth mentioning here that a TCP/IP-UDP line line in the perception of the D2000 system is actually a UDP socket, which is a logical device to support communication of individual stations. It is not possible to use stations with a different protocol on a line where stations with the SNMP protocol exist!

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Communication line configuration

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• Communication line category: TCP/IP-UDP.
• UDP parameters:
  • Host: There are three ways:
    1. The IP address of the particular network interface – datagrams will be transmitted and received only via this interface.
       Example:  192.168.1.10
    2. The symbolic name of a particular network interface.
       Example:  D2SRV_PRIMARY
    3. ANY or ALL -the configured UDP port is opened on all available network interfaces. An optimal network interface should be used for communication based on routing tables. The reception of messages will be performed on all network interfaces.
  • Port: UDP port number (0 through 65535) from which the D2000 KOM process sends requests and receives the responses. If the value is 0, the port number is assigned automatically by the OS.
    Note: Ports 161 and 162 are the standard UDP ports used in SNMP, but they are often reserved for SNMP agents - that is why it is recommended to choose different ports. Problems can occur with value 0 (zero) if the network uses firewalls and other security measures. Then, a specific port needs to be configured on the firewalls so that the packets from this port are passed via through the firewalls.

Note:
If SNMP protocol needs to run in a redundant system, where two instances of the D2000 KOM process are running concurrently on two different computers and the IP address cannot be positively determined in the line configuration, it is appropriate to choose „ANY“ or „ALL“ configuration option or to name the network addresses identically as e.g. SNMP_LAN and assign them a correct IP address in the hosts file of each computer. See example:

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• Communication protocol: SNMP Manager.
• Station's address: it is defined in the format IP_address1[:port1], IP_address2[:port2].

IP_address may be set in decimal dotted notation (e.g. 192.168.0.1) or as a name (e.g. SrvMoxa1), which assumes address translation by means of DNS or a hosts file. Address1 and Address2 concern the existence of primary and backup lines/routes. Address 2 is usable, for example, for a server containing two network interface cards, which is connected to two different network segments available via two different network paths.

Port is a number in the range 1..65535 on which an SNMP agent expects communication to take place. As the default (if not statedconfigured, or set to 0) port, the standard port 161 will be used.

Note:

• If the line has only a primary IP address configured (numerical or symbolic), UDP packets are sent from this address to both IP addresses of the station. One numerical primary IP address of the line + two IP addresses of the station are valid for a network topology where the local network is non-redundant, but the remote network (where the station is located) is accessible via two redundant communication paths.
• If the line has both IP addresses configured, UDP packets to IP_address1 leave from the primary IP address of the line, and UDP packets to IP_address2 leave from the backup IP address of the line.
  The situation when, e.g., IP_address1 is not configured conforms to the topology when the station is connected to a backup communication path only.

Protocol
The employed version of the SNMP protocol – one of the options can be selected:

• SNMP_V1 – the oldest version – does not support any secured access to the SNMP agent. It only distinguishes the objects that are freely accessible (public) and those belonging to a restricted group (private).
• SNMP_V2 – a version that supports authentication to access individual data types - an agent might (not) provide a particular set of data for an anonymous user (a manager,...) and different data for a user whose identity has been verified by entering a correct name and password.
• SNMP_V2C – the same as SNMP_V2 – the D2000 system does not distinguish these variants.
• SNMP_V3 – so far the latest protocol version – besides functions provided by SNMP_V2C, supports functions for authentication and encryption. It requires entering the name of an authentication server and authentication keys , to authenticate prior to communication with an agent, and keys for encrypting communication.

SNMP_V2, SNMP_V2C, and SNMP_V3 are not supported yet. Neither the writing into the SNMP agent nor reading MIB branches as a table (structured I/O tags or directly entered structure entries) are is supported.

Station protocol parameters

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Address1: Address of I/O tag. The address specifies the OID (Object identifier) of an object. It is displayed in a numerical format, e.g., 1.3.6.1.2.1.1.1.0. The address can also start with a dot, which is ignored, unless the Address is displayed in number format Root parameter is set (e.g., .: 1.3.6.1.2.1.1.1.0),

An I/O tag with such an address defined like that will all be read on a line, that is just operational (a primary or a backup line is determined according to the result of reply to previous request or possibly could be switched manually).via a network path, which is currently operational (a primary or a backup line is determined according to the result of a reply to a previous request, or possibly can be switched automatically).

If it would be necessary to have information on whether I/O tag with the address set by this way will be red always in active line (primary line, if this line is not available, then in case of need the backup line is automatic switched).
Information on availability of the primary or backup IP address of device can be found out using by so the device is available, it is possible to use the so-called forced addressing - just select by selecting the option Only Primary, respectively Only primary or Only secondary. Thus we This will ensure , that value acquisition of the I/O tag is required on that line only. The option Both is default one, when value will be acquired only from the primary, respectively, secondarystation address. The Both option is the standard option, where the values of the I/O tags are acquired obtained continuously on both linesfrom both addresses of the station (if they are configured). The Passive option Passive indicates, that this means that the value of the I/O tag is not read directly called, but its value is acquired obtained indirectly as a copy of a the value of another I/O tag with the same address, but in the state active mode, e.g., Only primary.

If I/O tag, with entered the object with a specified OID address , does not exitexist, the SNMP agent returns an error code with a different OID address (because the object with the required OID dos does not exist), and therefore, the communication will be denoted as unsuccessful. The I/O tag passes to the „Unknown value“ state. If it is necessary to indicate the line status by value change and not by the validity of the object's value, the object of DI type can be created, an integer value (e.g. UpTime) can be asked for and an automatic number to boolean conversion can be utilisedutilized, where 0 is converted to false and the others other values to True. The object properties can be then adjusted I/O tag can then be configured to use a substitute default value and to set the default to False. Then the object may acquire only the values True or False in dependence , depending on the object's availability in the SNMP agent.

The I/O tag with an address starting with %IGNORE will be ignored.