SNMP (Network Equipment · UPS)
SNMP v2c — reads infrastructure equipment such as switches, routers, UPS units, and servers (UDP 161). It's not for PLCs, but when you want to see the equipment that supports the plant on the same screen, this is what you use.
| Scenario | Which card to use |
|---|---|
| Switch · Router · UPS · Server · NAS | SNMP (this page) |
| Industrial PLC | Modbus TCP · OPC-UA |
| CNC machine tools | MTConnect · FOCAS |
Often the cause of equipment stoppage isn't the equipment itself but the network or power supply. If you put the UPS battery level and switch port errors on the same timeline as the equipment data, that diagnosis gets faster.
Registration Form Input Values
| Input field | What to enter | Example |
|---|---|---|
| IP address | Equipment management IP | 10.20.30.1 |
| Port | Standard 161 | 161 |
| Collection interval | Polling interval (ms) | 10000 (keep it long for infrastructure metrics) |
Options
| Option | Default | What it is |
|---|---|---|
community | public | SNMP community string |
request-timeout | 2000 | Response timeout (ms) |
public as-isEven if read-only, the community string is a password. Create a separate read-only community on the equipment, and make sure port 161 is not open outside the management network.
PLC Address Notation for Tags — OID
The PLC address of a tag = OID (dotted notation). The leading . is optional.
| OID | What it is |
|---|---|
1.3.6.1.2.1.1.3.0 | sysUpTime — time the equipment has been powered on |
1.3.6.1.2.1.1.5.0 | sysName — equipment name |
1.3.6.1.2.1.2.2.1.10.1 | ifInOctets.1 — received bytes on port 1 |
1.3.6.1.2.1.2.2.1.8.1 | ifOperStatus.1 — link status of port 1 |
🔴 Don't forget the index at the end. Scalar values take .0, table values take .<인덱스>. 1.3.6.1.2.1.1.3 is a branch, not a value, so it returns empty.
For vendor-specific metrics like UPS or PDU, the OID is documented in that vendor's MIB documentation.
How Values Come In
| SNMP type | Value received |
|---|---|
| INTEGER · Counter32 · Gauge32 · TimeTicks | Number |
| OCTET STRING | String (hex if non-printable) |
| OID | Dotted notation string |
| IpAddress | a.b.c.d |
| noSuchObject · noSuchInstance · endOfMibView | Empty string |
A counter like ifInOctets is a continuously increasing total, so its value alone is not very meaningful. If you need a per-second increase, use a formula to take the difference → Apply Formula
When It Doesn't Work
| Symptom | What to check first |
|---|---|
| All values empty | Community string, SNMP-allowed IP list on the equipment |
| Only specific OID empty | Whether an index (.0 · .1) is attached, and whether the equipment supports that MIB |
| Intermittently empty | UDP can drop packets — increase request-timeout |