You should create a new 'Performance Counter' check. Select the 'Network Interface' performance object, and choose the relevant NIC card as the instance. Then, select your performance item(s), e.g. 'Bytes Received/sec, 'Bytes Sent/sec', 'Bytes Total/sec', 'Current Bandwidth', 'Packets Received/sec', etc.
Network Monitor > Monitoring Network
| Error codes |
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| Click here to view the full list of error codes |