Not sure which network monitoring tools fit your network? Most fall into three types: SNMP-based, passive and active. Match the type to the question you need answered.
| Item | Value |
|---|---|
| Main types of network monitoring tools | 3 (SNMP-based, passive, active) |
| SNMP polling port on the managed device | UDP port 161 |
| SNMP traps and informs port on the manager | UDP port 162 |
| Ways to monitor passively | 3 (network TAP, SPAN port, flow-based protocols) |
| Active monitoring method | Continuous synthetic monitoring |
Figures come from NetBeez and Kentik, both vendor guides. Details can change, so check the source before you rely on them.
What network monitoring tools actually do
A monitoring tool watches your network and tells you when something is wrong, ideally before users notice. It answers basic questions: is a device up, is a link saturated, who is using the bandwidth, and is an application reachable?
Good monitoring turns vague complaints such as “the network is slow” into a specific, measurable finding: which link, which device, which time, which application. That shortens troubleshooting and gives you evidence for capacity decisions.
No single technique answers all of those. That is why the market splits into categories, and why many teams run more than one kind side by side.
The tools usually sit inside a wider toolset for configuration, inventory and automation. For that bigger picture, see our guide to network management software.
The three main types
NetBeez describes it this way: “There are three main types of network monitoring tools: SNMP-based tools Passive network monitoring Active network monitoring”. Each has its own job and its own blind spots.
- SNMP-based tools ask devices about their own health.
- Passive tools observe real traffic as it crosses the network.
- Active tools generate test traffic and measure the result.
Think of it as device view, traffic view and user-experience view. A healthy device can still sit on a slow path, and a quiet link can still hide a failing application.
SNMP-based monitoring
The Simple Network Management Protocol (SNMP) is, in NetBeez’s words, “an Internet standard used to request information from a device like a router, switch, firewall, or server, about the status of its resources, such as CPU utilization, memory consumption, and network interfaces.”
A manager polls an agent running on each device, and the agent reports values from its management information base. If you work with those values directly, you will meet object identifiers (OIDs), which name each metric.
Kentik explains the ports: “SNMP relies on two standard ports, one for each direction of communication: UDP port 161 (polling and queries): The SNMP agent on a managed device listens on port 161.” Notifications go the other way: “UDP port 162 (traps and informs): The SNMP manager listens on port 162 to receive unsolicited notifications.”
Typical use cases:
- Up/down status for routers, switches, firewalls and servers.
- CPU, memory and interface counters, graphed over time for capacity planning.
- Trap-driven alerts when a device raises its own event, such as a link going down.
Security matters here too. SNMP exposes detailed device data, so restrict which hosts may poll, avoid default community strings, and prefer the newer protocol versions that support authentication and encryption.
The weakness is scope. SNMP tells you how a device feels, not what users experience, and frequent polling of a large estate adds load.
Passive monitoring and flow data
Passive monitoring, per NetBeez, “relies on intercepting network traffic to identify network activity, links utilization, and application performance.” It can show which users, applications and protocols create the traffic.
The same guide says: “There are three ways to passively monitor a network: network TAP, SPAN port, and flow-based protocols.”
- A network TAP is a hardware tap that copies traffic from a link.
- A SPAN port mirrors traffic from a switch to a monitoring port.
- Flow-based protocols export summaries of conversations from routers and switches.
Flow is the lightest option. Kentik notes that “NetFlow is a network protocol developed by Cisco Systems that collects metadata on IP traffic flows traversing a network device, such as a router, switch, or host.” Related formats such as sFlow and IPFIX serve the same purpose.
When summaries are not enough, a packet analyzer lets you inspect individual packets, usually on a TAP or SPAN feed.
Active and synthetic monitoring
Active tools do not wait for traffic. NetBeez lists the active type’s function as “Continuous synthetic monitoring to measure end-to-end performance and proactive alert of network issues.”
Agents run scheduled tests such as ping, DNS lookups, HTTP requests and traceroute, then record latency, loss and availability. Because the tests run constantly, they catch problems at night or on rarely used paths.
Results are most useful when you keep history. A latency graph that shows a slow climb over weeks points to a different cause than a sudden spike, and you can only see that difference if the data was recorded.
Passive monitoring, by contrast, is described by NetBeez as reactive, since it “relies on real network traffic”. Active testing is the proactive counterpart.
It suits branch offices, cloud and SaaS paths, and Wi-Fi, where you cannot install SNMP agents on the thing you care about. The trade-off is that tests are only a sample of the user experience.
Choosing the right type for your use case
Start from the question rather than the product. The table below maps common needs to the best starting point.
| Question | Start with |
|---|---|
| Is this switch or firewall healthy? | SNMP polling and traps |
| Who is eating the bandwidth? | Flow data |
| Why is this one application slow? | Active tests, then packet capture |
| Is the cloud or SaaS path reachable? | Active synthetic tests |
This mapping is our editorial reading of the NetBeez guide’s three types; check that source before you rely on it.
A few habits make any choice work better. Write down what “healthy” looks like before you buy anything, so alerts reflect real thresholds rather than defaults.
- List the devices and paths that matter most, and monitor those first.
- Set alert thresholds from a baseline of normal behaviour, not from guesses.
- Route alerts to a person who can act, and retire alerts nobody reads.
- Review dashboards after every outage and add the check that would have caught it.
Small networks often begin with SNMP, because almost every device supports it. Add flow when capacity or security questions appear, and add active tests when users report problems your device graphs cannot explain.
Licensing, retention and alert noise matter as much as features. If budget is tight, the list of open source network monitoring tools is a reasonable place to trial each type before you commit.
This site is independent and not affiliated with any vendor named here. Tool descriptions are educational, not endorsements.
Frequently asked questions
What are the main types of network monitoring tools?
Show answer
NetBeez names three: SNMP-based tools, passive network monitoring and active network monitoring. They answer different questions, so they complement each other.
Which ports does SNMP use?
Show answer
Per Kentik, agents listen for polling on UDP port 161, and managers receive traps and informs on UDP port 162. Check your firewall rules allow both directions.
Is flow monitoring the same as packet capture?
Show answer
No. Flow records metadata about conversations, while packet capture keeps the packets themselves. Flow is lighter to run; capture gives deeper detail.
Do I need all three types?
Show answer
Not at first. Begin with the type that answers your most pressing question, then add others as gaps appear.
