---
type: Monitoring Guide
title: "How to Monitor Port Speed via SNMP (ifSpeed vs ifHighSpeed)"
description: "Read ifSpeed and ifHighSpeed, prefer ifHighSpeed on fast links, and detect a down-negotiated port against a baseline."
resource: "https://snmp-monitoring.info/monitoring/network/port-speed/"
tags: [monitoring]
timestamp: 2026-07-11T00:00:00Z
---

# How to Monitor Port Speed via SNMP (ifSpeed vs ifHighSpeed)

Read ifSpeed and ifHighSpeed, prefer ifHighSpeed on fast links, and detect a down-negotiated port against a baseline.

## Related concepts

- Up: [SNMP Network Monitoring: Interfaces, Bandwidth & Errors](/monitoring/network/index.md)

## Frequently asked questions

### What OID is interface speed in SNMP?

ifSpeed (1.3.6.1.2.1.2.2.1.5) gives speed in bits per second, and ifHighSpeed (1.3.6.1.2.1.31.1.1.1.15) gives it in megabits per second. Use ifHighSpeed as the reliable one, especially on 10G and faster links.

### Why is ifSpeed wrong on a 10G port?

Because ifSpeed is a 32-bit value in bits per second and tops out around 4.29 Gbit/s. Anything faster overflows that ceiling and reports incorrectly, so a 10G, 25G or 40G port must be read via ifHighSpeed, which uses Mbit/s and has plenty of headroom.

### How do I detect a down-negotiated port?

Record each port's expected speed as a baseline, poll ifHighSpeed regularly, and alert whenever the current value is below the baseline for that ifIndex — the classic case being a gigabit port that comes up at 100. Cross-check ifOperStatus so you only flag links that are actually up.

### Can SNMP show duplex?

Not from the standard IF-MIB — there's no duplex object there. Duplex is exposed by the EtherLike-MIB via dot3StatsDuplexStatus, if the device implements it. A duplex mismatch shows up indirectly as rising interface errors.

## Source

Concept generated from https://snmp-monitoring.info/monitoring/network/port-speed/ — the SNMP Monitoring vendor-neutral knowledge base. Content is limited to what that page states (no external claims added here).