SNMP Agent Connection Tag

Introduction

The SNMP Agent Connection Tag provides a connection to an SNMP agent.

The tags associated with the SNMP Agent Connection Tag can be read:

At a fixed interval.
On demand when requested by a Refresh Tag Command.
Both at a fixed interval and on demand.

Configuration Properties

The SNMP Agent Connection Tag supports the configuration properties of the Active Channel Tag plus these properties:

Property	Type	Version	Description
ScanInterval	TIME	1.3	The interval between each read. An interval value of zero (T#0s) disables periodic query execution. See Interval and Offset for information on how timed activities are scheduled.
ScanOffset	TIME	1.3	The offset added to the Interval to get the actual read time. See Interval and Offset for information on how timed activities are scheduled.
HostName	WSTRING	1.3	The network address of the SNMP Agent. Use any of the following: An IP address A node name A fully qualified domain name
PortNumber	WSTRING	1.3	The port number of the SNMP agent. The default value is 161.
SnmpVersion	USINT	1.3	The version of SNMP to use. The options are: 0 = SNMP Version 1 1 = SNMP Version 2c 2 = SNMP Version 3 For best security use SNMP Version 3.
GetRequestMaxObjects	UINT	3.78	The maximum number of objects to read in a GetRequest. Applies to SNMP Version 2c and Version 3.
ReadCommunity	WSTRING	1.3	The community password string used when the driver reads from the SNMP Agent. The default value is 'public'. Only applies when the SNMP Version is 1 or 2c.
WriteCommunity	WSTRING	3.53	The community password string used when the driver writes to the SNMP Agent. The default value is 'private'. Only applies when the SNMP Version is 1 or 2c.
V3UserName	WSTRING	3.48	The username for SNMP Version 3.
V3AuthProtocol	USINT	3.48	The Version 3 authentication protocol to use with the SNMP Agent. The options are: 0 = None 1 = MD5 2 = SHA1 For best security use SHA1.
V3AuthPassword	WSTRING	3.48	The password for SNMP Version 3.

SNMP Security

Use this table to understand SNMP security:

SNMP Version	Security	Comments
Version 1	Weak	The ReadCommunity and WriteCommunity strings are sent in plain text over UDP datagrams. Vulnerable to packet sniffing, and replay attacks.
Version 2c	Weak	The ReadCommunity and WriteCommunity strings are sent in plain text over UDP datagrams. Vulnerable to packet sniffing, and replay attacks.
Version 3 V3AuthProtocol None	None	Vulnerable to replay attacks.
Version 3 V3AuthProtocol MD5	Good	Password validation does not send the password in plain text over UDP datagrams. Resists replay attacks. Note: MD5 is now considered a weak hash algorithm.
Version 3 V3AuthProtocol SHA1	Good	Password validation does not send the password in plain text over UDP datagrams. Resists replay attacks.

Data Properties

The SNMP Agent Connection Tag supports the data properties of the Channel Tag plus these properties:

Property	Type	Description
ScanTimer	TimerStatus	The status of the scan timer.

Tag Commands

The SNMP Agent Connection Tag supports the tag commands of the Active Channel Tag plus these tag commands:

Tag Command	Version	Description
Refresh	1.3	Requests an immediate read of the tags associated with this SNMP Agent Connection Tag.

Note: Event triggered data reads (from the Refresh Tag Command) and periodic data reads (defined by the ScanInterval property) are independent. You can use the Refresh Tag Command, or the ScanInterval property, or both to determine when the tags are read.

Relationships to Other Tag Types

The SNMP Agent Connection Tag builds on the features of these tag types:

Further Information

Interval and Offset

To learn how activities are scheduled using Interval and Offset.

I/O Analog Data Point Tag

To learn about the I/O Analog Data Point Tag that can be associated with the SNMP Client Tag.

I/O Digital Data Point Tag

To learn about the I/O Digital Data Point Tag that can be associated with the SNMP Client Tag.

I/O String Data Point Tag

To learn about the I/O String Data Point Tag that can be associated with the SNMP Client Tag.

I/O Word Data Point Tag

To learn about the I/O Word Data Point Tag that can be associated with the SNMP Client Tag.

I/O Double Word Data Point Tag

To learn about the I/O Double Word Data Point Tag that can be associated with the SNMP Client Tag.

I/O Long Word Data Point Tag

To learn about the I/O Long Word Data Point Tag that can be associated with the SNMP Client Tag.

SNMP Client Driver

For an overview of the SNMP Client Driver.

Alarm Conditions

To learn about abnormal conditions in SCADA applications.

Glossary

For the meaning of terms used in Fernhill SCADA.