LAN dropping to 100Mbps from 1000 with TL-SG108E
My network uses a 5-port smart switch (TL-SG105E) to distribute 2 subnets and is configured for port based VLANs. VLAN 1 uses two of the ports and VLAN 2 uses the other three ports. VLAN 1 is cabled to my main router (AX55) and VLAN 2 is cabled to the ISP’s router and is used for IPTV. Both routers are located on the third floor of a 3-story home. The switch is located on the ground floor. Two CAT6a cables connect the two floors via wall jacks on each floor, i.e., wall jack to wall jack with nothing in between. The wall jacks are also CAT6a.
In order to give me some extra free ports, yesterday I swapped the 5-port switch for an 8-port model (TL-SG-108E). To my surprise the VLAN 1 speed dropped to 100Mbps. To isolate the problem, I did the following:
1. Ran a long CAT6a cable down the stairs in order to connect the AX55 directly to the switch. Everything was OK at 1000Mbps.
2. Reinstalled the 5-port switch using the original wiring. Everything OK at 1000Mbps.
3. Tried a different 5-port switch (same model). Everything still OK.
4. Installed the 8-port switch. Speed dropped to 100Mbps. I tried each port on the switch to see if it was a port problem. No luck.
5. I tried a different CAT6 cable (3m) from the wall jack to the switch. Speed came back to normal at 1000Mbps. This would normally indicate a cable problem. The cable was checked with a network cable tester and found to be OK, no shorts, opens, or crossed wires. It was also tested again with the 5-port switch reinstalled and everything was again OK at 1000Mbps.
6. Reinstalled the 8-port switch and the new cable between the wall jack and the switch. Everything is OK at 1000Mbps and has been running some 24 hours.
I do not understand why 2 different 5-port switches work just fine and the 8-port switch has a problem with the same network wiring. Has anyone else seen this? It is confusing and does not seem logical. It appears that the TL-SG108E is “more sensitive” when it comes to port speed negotiation.
I am debating on whether to return the switch to the vendor and any feedback may help me to make that decision.