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A faulty Ethernet cable can disrupt a home connection even when its link light is on. Before changing router settings or replacing equipment, check the plugs and ports, then compare the connection with a cable you know works. If that fixes the problem, the original cable is a strong suspect; if it does not, continue testing the device and the rest of the network path.
How to check whether an Ethernet cable is the problem
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Confirm the connection path
Trace the cable from the affected device to the router or switch. Make sure each plug is fully seated and connected to the intended ports: the computer’s Ethernet port and a router’s LAN port, not its WAN/Internet port. Microsoft’s Ethernet troubleshooting guide starts with checking the cable and ports.
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Look for physical damage
Check the plugs and ports for visible damage, dirt, or missing pins, and look for tight bends or signs that the cable has been crushed or pulled. A visual check can reveal an obvious problem, but it cannot prove that a cable is sound. Cisco notes that physical stress can leave a cable marginal even if a link remains active (Cisco LAN switching troubleshooting).
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Swap in a known-good cable
Temporarily replace the suspect cable with one that works elsewhere. Repeat the same activity or connection so the comparison is meaningful. If the issue disappears, the original cable is implicated. A spare of unknown condition is a less useful test than a cable already confirmed to work; both Microsoft and Cisco recommend trying another or known-good cable (Microsoft; Cisco).
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Test another device
If the cable swap does not help, connect another device to the same network path if possible. If that device works, the original computer, its Ethernet adapter, or its port becomes a stronger suspect. If neither device works, the router, another part of the connection, or the internet service may be involved. A failed cable swap alone does not identify which one.
Why a link light does not rule out a bad cable
A link light shows that the connected equipment has established a physical link; it does not confirm that every wire and connection is performing reliably. Cisco describes broken wires and marginal cables as possible causes of Ethernet trouble, including cases where a link remains present. Packet errors can also point to a physical-layer problem, but they are a clue rather than proof that the cable is at fault.
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When to use an Ethernet cable tester
For a short removable cable, swapping in a known-good cable is usually the simplest fault-isolation check. A tester is more useful when the suspected fault is in a wall jack, a long installed run, or wiring you cannot easily replace for comparison.
Basic wire-map verification and standards certification are different. A simple verifier can check whether wires are connected in the expected order, but that result does not establish that a run meets all specified transmission-performance parameters. Fluke Networks distinguishes verification and troubleshooting tools from certification instruments in its network engineer tools guide.
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Which Ethernet cable category fits your speed and distance?
Choose cable based on the link speed your equipment supports and the length of the run—not simply the largest category printed on the package. NETGEAR’s published guidance, updated July 7, 2025, gives these category and distance figures:
| Cable category | Published speed and distance guidance | Practical context |
|---|---|---|
| Cat 5 | 100 Mbps up to 100 m (328 ft.) | Below the gigabit capability of Cat 5e. |
| Cat 5e | 1 Gbps up to 100 m (328 ft.) | NETGEAR recommends it for networks at 1 Gbps or less. |
| Cat 6 | 10 Gbps up to 55 m (180 ft.) | NETGEAR recommends Cat 6 or better when the ISP and wired devices support multi-gigabit speeds. |
| Cat 6A | 10 Gbps up to 100 m (328 ft.) | Relevant when the equipment and run length call for its higher-speed, longer-distance guidance. |
These are category/application guidelines from NETGEAR Support, not a promise that every cable, connector, installation, or endpoint will deliver the listed rate. A higher-category cable will not raise an internet plan’s speed beyond the service or equipment limits, and it cannot fix a faulty router or computer port.
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- 40Gbps Speed, Wide Compatibility This Cat 8 Ethernet cable supports up to 40Gbps data transfer and 2000MHz bandwidth for fast, reliable internet performance. Standard RJ45 connectors are backward compatible with Cat7, Cat6, Cat6a and Cat5e devices, including routers, modems, switches, gaming PCs, PS5, PS4, Xbox, smart TVs, laptops and printers.
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What to do if changing the cable does not help
Keep isolating the connection instead of assuming the cable is the cause—or that the router or ISP must be at fault. Compare another device on the same path, inspect the ports and adapter, and, for installed wiring, test the run or compare it with a known-good path. If several devices have the same issue, the fault may lie farther upstream; Microsoft’s troubleshooting guidance also identifies the router, ISP, or adapter as possibilities.
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