@bolvar That switch cannot change the UDP port for remote log. It uses syslog protocol. UDP 514 is the standard port for that protocol.

@JF1995 If try COPEL<->WAN2, SERCOMTEL<-> WAN1, will both WAN ports get 300Mbps? Just for checking if the WAN2 has problem.

@SKCBD5 As I knew, TP-Link many routers support WDS function. There are two FAQ in TP-Link website. And also has some routers support WISP function. It seems that WISP is similar to WDS....

@glnzglnz I noticed that its power supply is changed to 5VDC/0.6A. The original is 9VDC/0.6A. Maybe still has other improvement. But unfortunately I don't know more detail.

@glnzglnz The latest version of TL-SG105 is version 5.0. Maybe the website of your region did not update the information.

@Yannt According to your test result, the problem may happen on ER5120. Do you have any settings on ISP box, like MTU or port forwarding? If ER5120 uses the same setting, I haven't solution as well....