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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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Protocol SNMP protocol (Simple Network Management Protocol) is used for monitoring and administration of network components. It allows detection of the network devices' status and changing of their settings. In an application, it is possible to monitor the functionality of e.g. routers, switches, computers, etc.
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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 range 1..65535 on which an SNMP agent expects communication to take place. As the default (if not stated, 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 line + two IP addresses of the station are valid for 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.
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| Keyword | Full name | Description | Unit | Default value | ||||||
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| Wait Timeout | Timeout The timeout period for the response to the read request. | ms | |||||||
| Retry Count | Number A number of re-sent read requests, before the read reading is considered to be unsuccessful and another I/O tag will be queried. | - | |||||||
| Max Error Count | Maximum count of unsuccessful read requests, until the station changes its value to StCOMERR state. A successful value delivery nullifies all counters and puts the station back into StON state. | - | |||||||
| Trace Level | The same meaning as parameter Trace Level on a line, but this setting is valid for the particular station. However, the higher value of a line parameter Trace level takes precedence. Note: Debugging of incoming packets is influenced by the line parameter Trace Level because at the time of reception it is still unknown which station the packet belongs to. | - |
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Address1: Address of I/O tag. Address . The address specifies the OID {Object identifier) of an object. It is displayed in number a numerical format, 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 via a linenetwork path, that which is just currently operational (a primary or a backup line is determined according to the result of a reply to a previous request or possibly could can be switched manuallyautomatically).
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 called forced addressing - just select the option Only primary or Only secondary. Thus we ensure, that value acquisition of I/O tag is required on that line only. The option Both is default one, when the values of I/O tags are acquired continuously on both lines. The option Passive indicates, that this If it would be necessary to have information on whether the primary or backup IP address of the device is available, it is possible to use the so-called forced addressing by selecting the option Only Primary, resp. Only backup. This will ensure that the I/O tag value will be acquired only from the primary, resp. backup station address. The Both option is the standard option, where the values of the I/O tags are obtained continuously from both addresses of the station (if they are configured). The Passive option 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 I/O tag can be then adjusted 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.
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Request: Default value Get causes the values will to be read by a Get SNMP request Get.
Some devices have problems to give value providing values by Get, if it is the item of fieldthe Get request if the object is an item of an array. Then, you must configure the type of request GetNext and the address should be OID of the previous object (to find the address, use java the Java application MIB Browser (http://tl1.ireasoning.com/mibbrowser.shtml) that reads the whole tree of values and detects the OID address of the previous object).
Time delay: Offers a possibility to set a delay period for particular I/O tags – to optimize the network's load. This time is added to the current time after a successful call and next call reading of the I/O tag's value and the next request will be processed as soon as the current time is greater than or equal to the time calculated in this way.
If the object's value is unknown, the object will be included in communication in the next call periodic request (according to the time parameters of the station) regardless of the delay time.
Parameter Time The time delay parameter does not influence the processing of TRAP messages if the TRAP has the same address than address of Ias the /O tag.
After receiving the value from the SNMP agent, the conversion will be done according to the real type of value in the SNMP protocol and the required type in the D2000 system. If it is not possible to carry out the conversion, the value will be in unknown state invalid and a report about the wrong conversion will be logged into a trace file.
ASN1 value type: Specifies, the value type in the SNMP agent's response. It also determines applicable conversions. The value type can be detected in the MIB database (note MIB : MIB database browser is not a part of the solution). One of the freely available browsers can be used and desired data format can be set based on the obtained information. It is recommended to use java application the MIB Browser Java application (http://tl1.ireasoning.com/mibbrowser.shtml).
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| Integer | input value - expected as a signed integer number (up to 64bit *) |
| Unsigned | input value - expected as an unsigned integer number (up to 64bit *) |
| Float | input value - expected as a floating-point number (float, a longfloatlong float) |
| TextxtText | input value - text string |
| IP address | the input sequence of bytes interpreted as a sequence of numbers separated by a dot – the sequence is converted to text |
| Hex text | the input sequence of bytes is interpreted as a sequence of hexadecimal numbers separated by a colon – the sequence is converted to text |
The value types IP address and Hex text can be applied to an arbitrary input data type, which will be further handled with as a sequence of bytes. E.g., the input value of text type with value "test@ipesoft.sk" can be interpreted in the following ways:
Text: "test@ipesoft.sk"
IP address: „112.101.114.105.99.104.64.105.112.101.115.111.102.116.46.115.107“7“
Hex text: „70:65:72:69:63:56:40:69:70:65:73:6F:66:74:2E:73:6B“
These methods were introduced to support cooperation with IP and MAC addresses of network interfaces.
* System D2000 support D2000 system supports values of objects in the maximum range of 32 bits for signed integer types. Therefore, if the number is bigger, then the maximum value of the 32-bit range will be assigned to it. If the input object of the D2000 system is of Ai type, the system will attempt to convert it to Real.
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The following table shows the supported conversions of value types:
- admissible supported conversion
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Protocol SNMP protocol also allows, except for cyclic value reading, to send messages about important events. This These messages are called Traps.
SNMP agent sends the Traps to the configured IP address and port (by default 162) which is configured (elementary simple devices support to send sending of Traps to one IP address and port, advance advanced ones send Traps to more addresses).
The parameter The Trap IP address parameter must by be configured to activate a task that receives the Traps on the port the Trap port.
Trap receiving is supported in the version V1 and V2C of protocol SNMP. Default mode - By default, one device send sends Traps to using one version of the protocol.
To receive Traps from a particular device, I/O tags with the following text addresses must be configured on the station (however, there is no need to configure all of them) must be configured on the station:
Text addresses of I/O tags for Traps in SNMP protocol, version V1:
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