Troubleshooting Deco M5 Wi-Fi Speed and Forcing 5 GHz on Linux

Overview

This guide explains common causes of reduced Wi-Fi speeds when using a Deco M5 system and provides methods to force Linux clients to connect to the 5 GHz band.

Part 1 — Why Deco M5 Shows 100 Mbps but Wi-Fi Devices Get Less

The Deco M5 has two auto-sensing Gigabit ports. If you see 100 Mbps on wired tests, it’s usually cable/negotiation (bad cable, old NIC, or port mismatch), not a hard limit of the Deco.

2. Devices Connecting to 2.4 GHz Instead of 5 GHz

Realistic 2.4 GHz throughput is typically 30–70 Mbps. Devices that connect to this band will not reach 100 Mbps.

3. Weak Signal or Poor Placement

Wi-Fi speeds drop significantly when the device has:

  • Physical obstructions
  • Long distance from the access point
  • Interference from appliances or neighboring networks

4. Wireless Interference

ISP routers or nearby Wi-Fi networks may broadcast overlapping channels, reducing throughput.

5. Double NAT or Incorrect Mode Configuration

Having both the ISP modem and Deco in router mode can introduce bottlenecks. Use Deco Router Mode with the ISP modem in Bridge Mode when possible.

6. Client Device Limitations

Older or lower-end devices may only support slower Wi-Fi link rates or use power-saving modes that throttle speeds.

Quick Diagnostic Tests

Check Wi-Fi Band

Verify if the device is connected via 5 GHz through the Deco app.

Speed Test Near the Deco

Test near the node; improved speeds imply a signal issue.

Wired Test

A wired test isolates whether the bottleneck is Wi-Fi or the Deco unit. Confirm the link is at 1 Gbps (e.g., ethtool eth0 | grep -i speed on a wired client).

Part 2 — How to Force 5 GHz on Linux

Linux may automatically prefer 2.4 GHz networks. The following methods force the system to use 5 GHz.

Method 1: Force 5 GHz Band via NetworkManager

nmcli connection modify <ConnectionName> wifi.band a
nmcli connection down <ConnectionName>
nmcli connection up <ConnectionName>

Method 2: Lock to a Specific 5 GHz BSSID

List nearby networks:

nmcli device wifi list

Modify the connection:

nmcli connection modify <ConnectionName> wifi.bssid <5GHz-BSSID>

Reconnect:

nmcli connection down <ConnectionName>
nmcli connection up <ConnectionName>

Method 3: Manually Connect to a 5 GHz Frequency (Testing Only)

sudo iw dev wlan0 connect <SSID> freq 5180

Check Supported Wi-Fi Bands

iw list | grep -A20 Bands

Troubleshooting Wi-Fi Performance on Linux

iw dev wlan0 link

Disable Wi-Fi Power Saving

sudo iw dev wlan0 set power_save off

Restart NetworkManager

sudo systemctl restart NetworkManager

Summary

Common Causes of Reduced Speed on Deco M5

  • 2.4 GHz band usage
  • Weak signal or interference
  • Device limitations
  • Wired link negotiating at 100 Mbps (cable/port mismatch)

Linux Fixes

  • Force 5 GHz band using NetworkManager
  • Lock to specific 5 GHz BSSID
  • Improve signal and placement