Today we will be discussing layer 2 switches and auto negotiation. Links on switches can operate at varying speeds such as 10, 100, or even 1000Mbps. Switches can also operate on half-duplex and full duplex. So say I have two switches but they’re running different settings but I want them to form a link together. What would happen? They will negotiate automatically using FLPs between speeds and duplex as part of the auto-negotiation process.
Once you plug in a link that connects two switches, they will begin to share “FLPs” which stand for fast link pulses. Fast link pulses are used by switches to advertise the capabilities of the specific link that the switches are sharing. Fast link pulses do what the name suggests, they send electrical pulses on a link, each pulse contains binary information on the devices capabilities such as speed and duplex. The receiving host on the other end of the link receives these pulses and compares the sender’s capabilities with their own before agreeing on settings. Once the two switches receive FLPs from each other, they then choose the fastest mutual speed and choose whether to operate on half-duplex or full duplex. The goal during auto-negotiation is to choose the highest speed that both switch links can do and full duplex. full-duplex is preferred because collisions are almost non-existent compared to half-duplex.
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