Ethernet and LAN Troubleshooting Guide

Ethernet Connection Basics

Understanding Cable Categories

Ethernet cables come in several categories, each with different speed and distance capabilities. Cat5e (Category 5 enhanced) supports speeds up to 1 Gbps over distances up to 100 meters and is still the most commonly installed cable in Indian homes and offices. Cat6 supports up to 10 Gbps over short runs (55 meters) and 1 Gbps at the full 100 meters, with better shielding against crosstalk. Cat6a extends the 10 Gbps capability to the full 100-meter distance and is the current recommendation for new installations. The cable category is printed on the outer jacket of the cable, so you can easily check what you are using.

All ethernet cables use RJ45 connectors, which are the clear plastic plugs at each end with eight colored wires visible inside. The connector has a small locking tab that clicks into the port. If this tab breaks off, the connector will not seat properly and can cause intermittent disconnections. Switches and hubs both provide multiple ethernet ports but work differently. A switch directs traffic intelligently to the specific device that needs it, while a hub broadcasts all traffic to every connected device. For any modern network, always use a switch rather than a hub.

Common Ethernet Issues

No Link Light (Cable or Port Issue)

When you plug an ethernet cable into a port on your router, switch, or computer, a small LED next to the port should light up to indicate an active connection. If this light does not turn on, either the cable is faulty, the port is dead, or the network adapter on the connected device is disabled. Start by trying the cable on a different port. If it works on another port, the original port may be damaged. If it does not work on any port, try a different cable. If a known-good cable also does not light up the port, check that the network adapter is enabled in your operating system. On Windows, open Network Connections from Control Panel and verify the ethernet adapter is not disabled.

Limited Connectivity or IP Address Conflict

If your computer shows a connected status but says "Limited" or "No Internet Access," the most likely cause is an IP address issue. Your device may have failed to obtain an IP address from the router DHCP server, or two devices may have been assigned the same address. Open a command prompt and run ipconfig to check your current IP address. If it starts with 169.254, your device is using a self-assigned address because it could not reach the DHCP server. Run ipconfig /release followed by ipconfig /renew to request a fresh IP address. If the problem persists, restart your router to clear its DHCP lease table.

Slow Wired Speeds

Ethernet connections that are slower than expected often come down to one of three issues: cable category limitations, duplex mismatch, or adapter settings. If you are using an old Cat5 cable (not Cat5e), your maximum speed is 100 Mbps regardless of your internet plan. A duplex mismatch occurs when one end of the connection is set to full duplex while the other is at half duplex. This causes collisions and dramatically reduces throughput. Check the adapter settings in Device Manager and ensure Speed and Duplex is set to Auto Negotiation. Also verify that the green link light (not just orange) is lit on both the port and the adapter, as orange typically indicates a 100 Mbps connection while green indicates 1 Gbps.

Intermittent Drops on Wired Connection

Intermittent ethernet disconnections are often caused by physical cable problems that are not immediately obvious. A cable that passes through a door frame, under carpet, or along a high-traffic area may have internal wire damage even if the outer jacket looks fine. Electromagnetic interference from power cables running parallel to ethernet cables can also cause packet loss. Keep ethernet cables at least 15 centimeters away from power cables, and use shielded (STP) cables in environments with heavy electrical equipment.

Step-by-Step Debugging

Cable Testing and Identification

If you suspect a cable fault but cannot confirm it by swapping, a simple cable continuity tester (available online for under 500 rupees) can check all eight wires for proper connections. The tester will show which wire pairs are working and whether the cable is wired as straight-through (for connecting a device to a switch) or crossover (for connecting two similar devices directly). Modern gigabit devices support Auto-MDI/MDIX and can use either cable type, but older equipment may require the correct type.

If you are crimping your own cables, use a quality crimping tool and follow the T568B wiring standard for consistency. The wire order from left to right (with the tab facing down) is: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. Ensure all eight wires are pushed fully to the front of the RJ45 connector before crimping. A poorly crimped connector is the most common cause of self-made cable failures.

Network Switch Troubleshooting

If multiple wired devices are experiencing issues simultaneously, the network switch may be at fault. Start by power cycling the switch: unplug it for 30 seconds and plug it back in. Check that port LEDs light up for connected devices. If some ports work and others do not, the switch may have failed ports. A network loop (where two ports on the same switch are accidentally connected to each other, or two switches are connected by multiple cables without proper configuration) will cause the entire network to slow to a crawl or stop working entirely. Check all cable connections to ensure there are no loops. Managed switches have loop detection features that should be enabled.

When to Upgrade Your Cabling

Consider upgrading your ethernet infrastructure if you are on a plan faster than 100 Mbps but still using Cat5 cables, if you are planning to upgrade to a gigabit or faster internet plan, if your cables are more than 15 years old and showing signs of degradation, or if you are moving into a new office and need structured cabling. For a professional structured cabling installation, Eyebroadband can assess your space and install Cat6a cabling with properly terminated wall plates and a patch panel for clean, reliable, future-proof networking.

Frequently Asked Questions