Guides
Ethernet Cables Explained: Cat5e, Cat6 and Beyond
Choose Cat5e, Cat6 or Cat6A for the link you need, and investigate 100 Mbps links, dropouts and cable swaps with controlled comparisons.
A damaged or unsuitable Ethernet cable can restrict a connection. A 100 Mbps link on a gigabit internet plan does not establish that the cable is faulty, though: the network card, adapter, dock or port may support only that speed. Check the actual wired path before buying a replacement.
Link speed is different from internet throughput
Link speed is what the network card and the directly connected router or switch negotiate. 1000 Mbps is 1 Gbps, but it does not promise an internet test result of exactly 1000 Mbps. The test method, server, other traffic and remaining path affect throughput. Confirm that the test uses Ethernet, and record any dock, switch, wall outlet and router LAN or WAN port along the path.
Choose a category for your intended link
- Cat5e supports 1000BASE-T, or gigabit Ethernet over copper. A correctly specified and installed connection can extend to 100 metres; a Cat5e label on one cable does not certify the entire installation.
- Cat6 also supports gigabit links. Its suitability for 10GBASE-T depends on length, the complete channel and crosstalk from neighbouring cables. A short run alone is not a 10 Gbps guarantee.
- Cat6A is a suitable option for new 10GBASE-T installations up to 100 metres when the complete connection meets the requirements. Local transfers to a NAS or another computer may need that link even with a slower internet plan.
- Both endpoints must support the intended speed. A higher cable category cannot make a 100 Mbps port faster. For fixed cabling, check the specifications of the cables, connectors, outlets and installation environment together.
Investigate low link speeds or dropouts one step at a time
- Record link speed before making changes. Windows can show it in Ethernet connection status; macOS provides Ethernet details in network settings. Menus vary with the version. Read the status without changing speed or duplex settings.
- Check the supported Ethernet speeds of the network card, adapter and ports in use. A router's advertised Wi-Fi speed may exceed its LAN or WAN port speed. Retain normal automatic negotiation; forcing 1 Gbps is not a reliable repair.
- Replace just the accessible cable with a short, suitable cable known to work. Keep the same computer and port. Compare link speed and disconnections; run internet tests separately with the same method and server, without your own simultaneous transfers or tests.
- If the problem remains, compare one other suitable LAN port or one other computer at a time. A separately tested path around an accessible outlet or intermediate switch must retain the router's protection. Avoid network loops and do not connect the computer directly to the internet to bypass protection.
Interpret a successful cable swap carefully
An improvement points towards the part of the connection you changed, but unplugging and reconnecting can also affect the contact or negotiation. If the original cable is undamaged and safe, a controlled return comparison can help confirm the difference. Visible damage or increasing CRC or FCS counters on supported equipment provide useful clues, but the port or network card may also be responsible. Age or a flat cable shape alone is not evidence of failure.
Buying a cable or asking for support
- Choose a cable with fitted connectors and documented category, length and intended environment. An inexpensive replacement may solve a fault, but price or a label cannot guarantee that outcome.
- For fixed installations, outdoor use or power over Ethernet, check the requirements of the specific equipment and installation. Use qualified help for installation and verification; do not improvise electrical wiring or grounding.
- Share port and adapter models, cable lengths, link rates and before-and-after comparisons privately with support. M-Lab NDT measures a TCP transfer along an internet path, not an isolated cable or cabling certification. It uses data, and M-Lab publishes measurement data including IP addresses.
When is replacing the cable enough?
If the replacement repeatedly restores the expected link speed and a stable connection under comparable conditions, keep it and monitor normal use. If the Ethernet link is already at the expected speed but the internet result is low, investigate the remaining path before buying a higher category. Persistent fixed-cabling problems call for checking the complete connection rather than promising that one cable will fix everything.