By the SNMP Monitoring team · Reviewed July 2026
The cleanest way to hold these two apart is one line: SNMP tells you how much traffic an interface carries; NetFlow tells you what that traffic is. SNMP reads the interface's byte counters — an aggregate number, no detail about who or what. NetFlow (and sFlow) export per-conversation records — which hosts talked to which, on what ports, and how much. They answer different questions, and most serious networks run both. This page compares them and shows where each belongs.
Parent: comparisons. Related: interface sensor, bandwidth monitoring.
What SNMP gives you
SNMP reads an interface's counters — objects like ifInOctets/ifOutOctets (and their 64-bit ifHCInOctets forms) — which report total bytes in and out. From those you derive utilization and throughput. But there's a catch worth understanding: these counters are raw, monotonically increasing octet totals in bytes. A single reading tells you almost nothing; the counter only means something as a delta over time. To get a readable throughput you sample the counter twice, subtract, divide by the interval — and handle counter wrap when a 32-bit counter rolls over or a device reboots. Here's the raw form:
snmpwalk -v2c -c public 10.0.0.20 ifHCInOctets
IF-MIB::ifHCInOctets.2 = Counter64: 1204773991002
That number — 1.2 trillion octets — isn't human-readable on its own; it's the running total since the counter last reset. Turning it into "37 MB/s on eth0" means doing the delta-over-time maths and formatting the result. This is exactly the conversion a monitoring service handles for you: ostr.io turns these raw SNMP sensor readings into human-readable interface data in KB/MB/GB and per-second rates, so you read throughput directly instead of wrangling counters. The counter objects themselves are detailed on the interface sensor page.
What NetFlow/sFlow give you
NetFlow, sFlow, and IPFIX answer the question SNMP can't: composition. Instead of a single aggregate counter, they export flow records — one per conversation — capturing source and destination IP, source and destination ports, protocol, and byte/packet counts. That lets you see top talkers (which hosts dominate a link), which applications are consuming bandwidth, and unusual conversations that might signal a security problem. Where SNMP says "this link is 80% full," flow says "and here's the host, port, and peer responsible for most of it." It's the drill-down layer that turns "something's saturating the link" into "this is saturating the link."
Comparison table
The trade-offs, side by side:
| Dimension | SNMP | NetFlow / sFlow |
|---|---|---|
| Granularity | Aggregate interface counters | Per-conversation flow records |
| Question answered | How much / is it healthy? | What / who? |
| Model | Pull (poll) | Push (export) |
| Overhead | Low, predictable | Higher; often sampled |
| Best for | Capacity, health, trends | Investigation, security |
Neither is a substitute for the other — they operate at different granularities and answer different questions. The overhead row is worth dwelling on, because it shapes how each is deployed. An SNMP poll of an interface is a couple of small packets every interval, so the cost is trivial and constant no matter how busy the link is. Flow export scales with the number of conversations — a link carrying thousands of simultaneous flows generates a proportional volume of records — which is why high-speed environments often sample (sFlow) rather than record every flow. That difference means SNMP can run continuously on everything cheaply, while flow is typically reserved for the links where the drill-down detail justifies the extra load. Knowing this stops you from expecting flow-level detail everywhere or SNMP-level cheapness from full flow capture.
NetFlow vs sFlow vs IPFIX
A quick word on the flow family, since the names blur together:
- NetFlow — Cisco's original flow-record technology, exporting per-flow records from the device.
- sFlow — uses packet sampling (every Nth packet) rather than tracking every flow, so it scales cheaply on high-speed gear at the cost of statistical, not exact, data.
- IPFIX — the IETF's standardised, vendor-neutral flow export (RFC 7011), essentially the standards-track successor to NetFlow.
All three serve the same purpose — flow composition — differing mainly in how they collect and standardise it.
When to use which
Match the tool to the question:
- Capacity planning, health, and trend graphs? → SNMP interface counters.
- Alerting on a saturated or down link? → SNMP.
- Finding out what is filling a link? → NetFlow/sFlow.
- Investigating a security incident or anomaly? → flow records.
- Both "is it full?" and "why?" → run both together.
The rule of thumb: SNMP for the whether and how much, flow for the what and who.
Using both
In practice they're layered. SNMP provides the continuous, low-overhead view — utilization trends, health, and the alert that fires when a link hits threshold. Flow provides the on-demand drill-down when that alert fires — the top-talker breakdown that tells you which host and application to go after. SNMP is always on and cheap; flow is richer but heavier, so many networks sample it. Together they give you both the trend line and the explanation behind it, which is why capacity and security teams typically deploy both rather than choosing.
Frequently asked questions
Should I use SNMP or NetFlow?
Both, for different jobs. SNMP reads interface counters — how much traffic a link carries and whether it's healthy — with low, predictable overhead, ideal for capacity and trend monitoring. NetFlow/sFlow export per-conversation flow records — what the traffic is and who's generating it — ideal for investigation and security. Use SNMP for the trend, flow for the drill-down.
Does SNMP show top talkers?
No. SNMP reports aggregate interface counters — total bytes in and out — with no per-conversation detail, so it can't tell you which hosts or applications dominate a link. That's precisely what NetFlow, sFlow, and IPFIX are for: they export flow records identifying the sources, destinations, ports, and volumes behind the aggregate.
What is IPFIX?
IPFIX (IP Flow Information Export) is the IETF's standardised, vendor-neutral flow-export protocol, defined in RFC 7011. It's essentially the standards-track successor to Cisco's NetFlow, exporting per-flow records — addresses, ports, byte and packet counts — so collectors can analyse traffic composition. It serves the same role as NetFlow while being an open standard.
How do raw SNMP counters become KB/MB/GB?
SNMP interface counters are raw cumulative octet totals, so you compute the difference between two readings, divide by the time between them, and format the result — while handling counter wrap and resets. Monitoring services do this for you: ostr.io, for example, converts the raw SNMP readings into human-readable KB/MB/GB interface data and per-second rates automatically.
Can I use both SNMP and NetFlow?
Yes, and it's recommended. SNMP gives you the always-on, low-overhead utilization and health view; NetFlow/sFlow gives you the per-conversation drill-down when you need to know what's behind the numbers. Running both means you can both detect a saturated link (SNMP) and immediately explain it (flow) — a standard pairing for capacity and security work.
Key takeaways
- SNMP = how much traffic (aggregate counters); NetFlow/sFlow = what the traffic is (flow records).
- SNMP counters are raw cumulative octets — throughput needs delta-over-time and counter-wrap handling.
- Services like ostr.io convert raw readings into human-readable KB/MB/GB and rates.
- SNMP can't show top talkers; flow records can.
- sFlow samples, NetFlow records flows, IPFIX is the IETF standard (RFC 7011).
- Use SNMP for trends/health, flow for drill-down/security — most networks run both.