10 - Interface Speed & Duplex Issues

Question 1

Interface speeds break into 2 groups = Speed & duplex

What are the speed options ?
What are the Duplex options ?

Answer 1

Speeds have 3 options = 10, 100, 1Gb

Duplex have 2 options = Full Duplex, Half Duplex

Question 2

By default ALL Interface are set to what speed and duplex ?

Answer 2

By Default all interfaces are set to Auto
(Hubs can only talk in half)

• Auto means they listen & check to see what the setting are on the cable & other side.

Based on checks they select what speed & duplex to use.

All the below will be by default Auto
Switch  	- Auto 
Pc 		- Auto
Router	- Auto
server	- Auto

Question 3

What should normally happen when both sides of interface are set AUTO ?

Answer 3

Normally both side will Auto detect and negotiate
speed = fine
Duplex = fine

(Hubs can only talk in half)
so device connecting to hub will be Half duplex

Question 4

What happens when 1 device is set Manually,

& other side is set to Auto detect ?

Answer 4

Speed - Left on Auto is fine
Duplex - left on auto is where the issue can happen

Most of the time Duplex is where they negotiate incorrectly

Question 5

why does Auto detect connecting to Manual

cause issues ?

Answer 5

To cater for old technology
e.i Hubs are always half duplex

Device auto Switch Auto
Result= speed fine, Duplex fine

Device Manually set Switch Auto
Result= speed fine, Duplex drops to HALF

Due to the Auto device side not being able to detect the other sides speed & Duplex as it set manually.
It drops to Half.

Question 6

What is the solution to duplex miss-match ?

Answer 6

If one side is set Manually - then set other side manually too. Manually set both sides !

But if they are meant to be set to auto - then set both sides to auto !