If Ethernet became slow after you added a switch, compare the connection directly to the router with the same computer connected through the switch. Check the negotiated link rate on both the router-to-switch and switch-to-computer links, then test cables and ports one at a time. This separates a slow Ethernet link from an internet-speed problem and helps identify whether the switch is actually responsible.
1. Compare a direct connection with the switched connection
Use the same computer and run comparable speed tests first through the switch, then connected directly to a router port that supports the rate you are checking. Keep the test conditions as similar as possible. Record the speed-test throughput and the Ethernet link rate separately: a speed test measures end-to-end internet performance, while the link rate reports the negotiated speed of an Ethernet connection.
If the direct connection is also slow, the switch may not be the cause. The router, internet connection, computer, or test conditions could be limiting the result. If direct performance is normal but the switched path is slow, concentrate on the switch path. TP-Link and Intel both recommend using a direct connection to a known-capable router port as a comparison: TP-Link’s unmanaged-switch troubleshooting guide and Intel’s guide to Ethernet links capped at 100 Mbps.
2. Check the link rate on both Ethernet segments
Inspect the computer’s Ethernet adapter status in your operating system. If your router reports port status, check that too. The path has at least two relevant links: router to switch, and switch to computer. A lower negotiated rate on either segment can constrain traffic, even if the other link is faster.
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For example, a 100 Mbps link where the router, switch, and computer are expected to support gigabit is a reason to investigate the cable, port, or negotiation. It does not, by itself, identify which part is faulty. Compare the reading with the direct-to-router baseline and check both segments before replacing equipment. TP-Link describes this 100 Mbps case as a sign that devices on a link are not communicating well: TP-Link Support.
3. Test cables, wall wiring, and ports
A cable problem can affect the computer-to-switch connection or the switch uplink to the router. Include wall jacks and in-wall cabling if they are part of the route; changing only the short cable beside the computer will not rule out a fault elsewhere in the path.
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- Reseat the Ethernet plugs at the computer, switch, and router.
- Replace one cable at a time with a known-good cable, then check the link rate and performance again.
- Try a different switch port and, if available, a different router port that supports the intended rate.
- If the route uses wall jacks or fixed wiring, test around those sections too. A cable tester can help check wiring or continuity, but a basic continuity check does not establish that a run will support gigabit performance.
Intel specifically advises checking the complete cable route, including connections before and after switches and wall jacks, and comparing with proven Cat 6 or better cabling: Intel Support. A known-good Cat 6 Ethernet cable is a useful diagnostic replacement if you do not already have one; the cable category alone does not guarantee faster internet or repair a faulty in-wall run. TP-Link also identifies nonstandard cabling and poorly secured conductors or connectors as possible causes: TP-Link Support.
4. Confirm device capability and negotiation settings
Verify that the router port, switch port, and computer’s Ethernet adapter each support the rate you expect. A gigabit-capable computer connected to a 100 Mbps switch port, for example, cannot establish a gigabit link on that segment.
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For gigabit Ethernet, leave speed and duplex on auto-negotiation at both ends unless the device documentation for your exact models directs otherwise. Intel identifies auto-negotiation as the correct Speed & Duplex setting for gigabit on its Killer adapters: Intel Support. TP-Link likewise recommends auto-negotiation for its unmanaged switches and matching behavior at the router and network adapter: TP-Link Support.
If you have manually set speed or duplex on a managed device, check both ends and consult the documentation for those specific models before changing the setting. Do not assume that forcing a speed on just one side will fix a negotiation problem.
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5. Separate local-network performance from internet performance
If the direct-to-router connection is normal, cables and ports have been checked, and the switched path is still slow, compare local traffic with internet traffic. If you have two computers, connect both to the switch with other devices disconnected and transfer a file between them. Treat this as a diagnostic comparison, not a universal speed benchmark.
- If the local transfer is healthy but internet tests remain slow, investigate the router or internet path.
- If local transfers are also very slow, the switch, its links, or the computers’ network connections deserve closer attention.
TP-Link describes this two-computer transfer as a way to help distinguish local switch-path trouble from an internet-side problem: TP-Link Support.
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6. Decide whether the switch is the likely cause
Change one variable at a time—first cables, then ports—so each comparison tells you something. If the same computer performs normally when connected directly to the router, but remains slow through the switch after those checks, the switched path is implicated. That still does not prove the switch itself is defective: its uplink cable, a port, or another connection in the path may be responsible.
With an unmanaged switch, do not expect a software setting to resolve a physical link or negotiation problem. If controlled comparisons continue to isolate the switch after cables and ports have been ruled out, contact its manufacturer or test with a known-good replacement. TP-Link recommends support if transfer speed remains substantially below the direct-router comparison: TP-Link Support.
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