Lessons · Network switches · fibre links
Why the link between buildings is fibre
Copper stops at about 100 metres and carries an electrical path between the two ends. Fibre carries light, so it goes kilometres and joins nothing electrically.
Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.
What it is for
Two buildings on a copper link share a ground, and during a storm that difference goes through your switches. Distance is the reason people quote; isolation is the reason it matters.
How to think about it
Anything leaving a building goes on fibre. Inside a building, copper to the desk and fibre between floors when the run is long, and label both ends, because an unlabelled fibre is untraceable.
Worked example
enableThe # prompt.
configure terminalInto configuration mode.
interface gi0/1The uplink, on a fibre module.
description Fibre to Building B, panel 3 port 7Where it goes AND where it lands. A fibre run cannot be followed by eye.
switchport mode trunkA trunk, because it carries every VLAN between the two buildings.
endOut.
show interfaces statusThe description is the documentation. Nothing else on the switch can tell you where that cable goes.
Your turn
Make the fibre uplink carry every VLAN.
switchport mode
Console into a switch
The trap
Running copper between buildings because it is cheaper and the distance is under 100 metres. The distance was never the whole reason.