I have a 500 Mbps internet plan and a TP-Link Archer AX1800 router, but downloads through the router usually top out just below 100 Mbps. Rebooting the modem and router, replacing Ethernet cables, checking QoS and parental-control settings, updating the router firmware, and checking my PC's network drivers did not initially solve the problem.
When I connect my PC directly to the modem, I get roughly 390 Mbps, so the service and PC seem capable of higher speeds. The router's WAN status sometimes shows 1000 Mbps Full Duplex, but it has also reverted to 100 Mbps Full Duplex. Since the WAN link is negotiating at 100 Mbps, devices connected through the router are limited even though the PC's LAN connection shows 1000 Mbps.
The PC uses the Intel I225-V Ethernet controller built into an Asus ROG Strix B550-F motherboard, with Speed & Duplex set to Auto Negotiation. I tested multiple Ethernet cables, including Cat 6, and wondered whether the router's WAN port, the cable, or the network controller was faulty. Is there anything else I should check before replacing the router?
3 Answers
The Intel I225-V and this router should be compatible, although some early I225-V revisions had auto-negotiation and link-stability problems. Updating the motherboard’s Ethernet driver is worth trying, but the fact that the connection speed changes between 100 Mbps and 1000 Mbps points more strongly to the physical link than to an internet setting.
Cat 8 is unnecessary here. A properly working Cat 5e or Cat 6 cable can handle a gigabit connection, so the important thing is whether the cable and connectors are making a reliable connection. Since the PC reaches much higher speeds when connected directly to the modem, the PC’s Ethernet controller is probably not the main problem.
The adapter is an Intel I225-V, and its driver is current. I also confirmed that Speed & Duplex is set to Auto Negotiation, so I’m focusing on the cable between the modem and router or the router’s WAN port.
Check the negotiated speed of the router’s WAN port first. If it says 100 Mbps Full Duplex, everything behind the router will be limited by that link even if the PC-to-router connection shows 1000 Mbps. Try a known-good Cat 5e or Cat 6 cable, reseat both ends, and restart both the modem and router so they renegotiate the connection. The changing link speed is a strong indication of a cable, connector, or port problem rather than QoS or software.
That turned out to be the issue. A new cable made the WAN connection stay consistently at 1000 Mbps, and the router now delivers the expected speed. The original cable may not have been suitable, or the modem and router may not have renegotiated properly after the cable swap. I also connected the WAN port to LAN1 and the PC to LAN2 as a loopback test; all three router ports reported 1000 Mbps, so the ports appear to be working.
I’ll try the newer driver from the motherboard manufacturer. If that does not help, I’ll test the router and cables more directly before assuming the controller is defective.