Duplex Mismatch Detection I'm trying to create a lab on PT to learn about duplex mismatch. I made one end of Fast Ethernet half duplex and other end is full duplex. I was hoping to see an increment in late collisions which I studied that should indicate duplex mismatch. But the late collisions is 0. Any reason why this is happening?

Packet Tracer is a simulator aimed at CCNA level courses.

It doesn't accurately simulate real devices but only a subset of their functions. (and still those simulations aren't perfect).

I would not rely on this tool to test whatever part is not explicitly teached in Cisco courses that use Packet Tracer.

TLDR you cannot trust PT to correctly simulate this.