Damaged Switch Port Capped Gigabit Internet at 100Mbps, Slashing Speeds by 90%
Updated
Updated · How-To Geek · Jun 15
Damaged Switch Port Capped Gigabit Internet at 100Mbps, Slashing Speeds by 90%
3 articles · Updated · How-To Geek · Jun 15
Summary
100Mbps speed tests on a gigabit plan traced back to a single damaged Ethernet port on a gigabit switch, not the modem, router or ISP connection.
LAN testing with OpenSpeedTest showed devices behind the suspect link dropping to 100Mbps, while direct connections and other switch ports still delivered about 1Gbps.
That exact 100Mbps ceiling pointed to Ethernet auto-negotiation falling back from gigabit after a bad port or wire pair failure, since 100BASE-TX needs only 2 of 4 wire pairs.
The troubleshooting path was to map each link, check negotiated adapter speeds, test local throughput with OpenSpeedTest or iPerf3, then swap cables or bypass hardware one piece at a time.
The case underscores that a $10-$15 savings on cheap cables or switches can bottleneck an entire home network, because the slowest link sets the maximum speed for every device behind it.