How to Diagnose and Fix Network Speed Issues by Adjusting MTU Size

✨ Quick Answer

Intermittent network speed issues, interrupted downloads, or the inability to load certain secure web portals often occur due to a poor configuration of the Maximum Transmission Unit (MTU) size of your network card. If your provider requires packages smaller than your system's standard, intermediate routers must fragment the data, degrading performance.

Quick Diagnostics

Cause

Misconfigured MTU causing packet fragmentation

Solution

Set MTU to 1500 (or 1492 for PPPoE): ip link set dev eth0 mtu 1500

Cause

Failed network speed auto-negotiation

Solution

Force Gigabit speed: ethtool -s eth0 speed 1000 duplex full autoneg on

Intermittent network speed issues, interrupted downloads, or the inability to load certain secure web portals often occur due to a poor configuration of the Maximum Transmission Unit (MTU) size of your network card. If your provider requires packages smaller than your system's standard, intermediate routers must fragment the data, degrading performance.

Step-by-Step Solution

1. 1

   Step 1: Diagnosticar la fragmentación de paquetes mediante pruebas de Ping

   We are going to find the maximum packet size that your network can transfer without needing to split the data. Run the test by subtracting the 28-byte IP/ICMP header from your target:

   BASH Copy

   # Probar el tamaño de paquete en Linux (ejemplo para 1472 bytes de datos)
   ping -M do -s 1472 8.8.8.8
   

   (Si la terminal te responde Packet needs to be fragmented but DF set, significa que el paquete es demasiado grande. Reduce el número en incrementos de 10 hasta encontrar el valor exacto que responda sin fragmentar, por ejemplo 1420 bytes, y súmale los 28 bytes de cabecera: 1420 + 28 = 1448 MTU).

2. 2

   Step 2: Aplicar el tamaño de MTU óptimo en tu tarjeta de red

   Once the correct value is detected, configure your operating system's network interface (replace eth0 with your active card):

   BASH Copy

   # Cambiar el MTU temporalmente en Linux
   sudo ip link set dev eth0 mtu 1448
   
   # Verificar que los parámetros de red se hayan actualizado
   ip link show eth0