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How does collision happen on half-duplex switch port? Possible?
FreddyIW
Member Posts: 27 ■□□□□□□□□□
in CCNA & CCENT
Can collision happen on half-duplex switch port? How? 
Let's say PC A and PC B are connected to a Switch on port fa0/1 and fa0/2 respectively. I set port fa0/1 and fa0/2 and both PC NICs to half-duplex mode.
How does it collide? UTP Cables use 2 TX and RX each so the frames are still transmitted and received on different wires.
What are the differences with full-duplex then?
Let's say PC A and PC B are connected to a Switch on port fa0/1 and fa0/2 respectively. I set port fa0/1 and fa0/2 and both PC NICs to half-duplex mode.
How does it collide? UTP Cables use 2 TX and RX each so the frames are still transmitted and received on different wires.
What are the differences with full-duplex then?
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Simrid
Member Posts: 327
Correct me if i'm wrong however, full duplex allows synchronous transmission. The means that both PC's can send and receive data at a single time. With half duplex, what if both the pc's try to send at the same time? I believe that is when a collision would happen.Network Engineer | London, UK | Currently working on: CCIE Routing & Switching
sriddle.co.uk
uk.linkedin.com/in/simonriddle -
OptionsFreddyIW
Member Posts: 27 ■□□□□□□□□□
Correct me if i'm wrong however, full duplex allows synchronous transmission. The means that both PC's can send and receive data at a single time. With half duplex, what if both the pc's try to send at the same time? I believe that is when a collision would happen.
But the UTP cables transmit and receive on different wires? Why does collision still occur even with half-duplex? -
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OfWolfAndMan
Member Posts: 923 ■■■■□□□□□□
While in full duplex you can transmit and receive simultaneously, half duplex means you can only do one or another at a time. However, switches isolate collision domains per port, so collisions don't typically happen, unless you have some faulty hardware. However, if you're running a hub or a bridge, then yes you could have collisions and CSMA/CD will be utilized for when a collision occurs.:study:Reading: Lab Books, Ansible Documentation, Python Cookbook 2018 Goals: More Ansible/Python work for Automation, IPSpace Automation Course [X], Build Jenkins Framework for Network Automation [] -
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H3||scr3am
Member Posts: 564 ■■■■□□□□□□
Another misconfiguration that causes collisions as I understand is when the ports are set to full duplex, but the device is only half duplex, this causes a collision every time the full duplex device sends something. It was covered in my CCENT Exam cram book. -
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pevangel
Member Posts: 342
You're under false impression that the cable dictates what the NIC uses for transmit and receive. It's just a set of wires. A NIC in half duplex will send and receive on the same pair of wires even if there are other pairs available. -
OptionsOfWolfAndMan
Member Posts: 923 ■■■■□□□□□□
H3||scr3am wrote: »Another misconfiguration that causes collisions as I understand is when the ports are set to full duplex, but the device is only half duplex, this causes a collision every time the full duplex device sends something. It was covered in my CCENT Exam cram book.
This is correct as well. You will see a flashing Amber/green light on a port when this happens:study:Reading: Lab Books, Ansible Documentation, Python Cookbook 2018 Goals: More Ansible/Python work for Automation, IPSpace Automation Course [X], Build Jenkins Framework for Network Automation []
