When a network fault makes no sense, suspect the cable. Not because cables are glamorous - because they are bent, crushed, chewed, and bought for the price of a cup of tea, then expected to carry gigabit perfectly for a decade.
Technicians learn this the hard way: the cable is the most lied-about component in networking. It looks like a cable, it clicks like a cable, it passes a basic continuity beep - and still cannot carry gigabit, or drops the link whenever the desk moves. This page explains the three classic traps - the two-pair cable, copper-clad aluminium, and the bad crimp - and how to stop guessing.
Plenty of cables - especially the thin free ones bundled with routers and the leads inside old telephone-style installs - contain only two pairs (four wires). Two pairs is everything 100 Mbps needs, so these cables worked silently for years. The day you upgrade to gigabit internet or a gigabit switch, the same cable becomes a hard ceiling at 100 Mbps, and sometimes an unstable one. Peek at the plug against the light: a proper cable shows eight coloured wires entering eight contacts. Four visible wires means two pairs - retire it from any gigabit job.
The cheapest 'Cat6' cables are often CCA - copper-clad aluminium: aluminium wire with a copper skin. CCA has higher resistance, breaks more easily at the plug, heats more under Power over Ethernet, and is not compliant with the cabling standard it pretends to meet. It may work on a 2-metre desk run and fail mysteriously at 15 metres. Flat ribbon cables have a different weakness: the pairs are not twisted the way the standard requires, so they pick up interference - fine on a quiet desk, flaky beside power cables and motors. None of this means 'buy gold-plated audiophile Ethernet'. It means buy a plainly labelled Cat5e or Cat6, pure copper cable from a maker who states it, and keep the receipt-level honesty: the genuine article is still inexpensive.
Hand-crimped plugs fail at the last millimetre: a conductor that stopped short of its contact, pairs untwisted too far back, or the jacket not gripped by the plug so every tug works the wires loose. The signature is a link that drops when the cable is touched, or works on one PC and not another because one socket's pins press a fraction harder. Wiggle-test gently while watching the link light. If the light flinches, the plug - not Windows - is your fault. Re-crimping with the jacket properly inside the plug, or simply using a factory-made patch cable, ends it.
Rule of the trade: in any unexplained network fault, the cable is replaced before anyone is allowed to say the word 'motherboard'.
See the adapter settings changed live, step by step, in the full Technical Anshu video.
Watch Full VideoHold the plug up to the light and count the wires entering it. Eight wires in different colours means four pairs - what gigabit needs. Four wires means two pairs, and that cable can never exceed 100 Mbps whatever the jacket printing claims.
No. A standards-compliant Cat5e or Cat6 pure-copper cable already carries gigabit perfectly; paying more buys durability, not speed. The trap is at the bottom of the market - CCA and two-pair cables sold under gigabit labels - not at the top.
Basic testers check continuity only. A cable can be continuous and still be electrically poor - untwisted pairs, CCA cores, a crushed section - so gigabit negotiation fails or the link flaps. Trust the swap test over the beep test for speed and stability faults.