What kind of damage to a cat 5e cable can cause Gigabit Ethernet to fail?

Question

Computer networks

I read that cat 5e is vulnerable to interference, poor crimping, insulation failure, etc. The question arose after a situation when a link was raised between a computer and a gigabit switch only by 100 megabits. After replacing the patch cord, the problem was solved, but visually the old one was in order. I would like to know the theory on this issue - the information is scattered, what exactly could be the cause of such degradation. I also read that cat 5 can be sold under the guise of cat 5e - is it probably in our time, or is a fake not so profitable anymore?

Answer 1

1. Too long
2. Poorly crimped. Visually, this is not easy
to determine.

Answer 2

I remember there was a topic that some low-quality wires can be made of copper-coated aluminum. And aluminum degrades over time. And hence the stories about the wires that crumble after 10 years of operation.