I’m experiencing an internet speed issue when connecting through the SFP+ port on my router.

My setup is as follows:

• Rogers 2 Gb internet service with a modem that has a 2.5 Gb Ethernet port

• TL-SM5310-T SFP+ module

• MikroTik RB5009UG+S+in (for testing) with SFP+ port and 2.5 Gb WAN port

• Omada Controller OM300

• TP-Link SG3428X switch connected via SFP+ using DAC

• DAC cable: TL-SM5220-3M

Test scenarios and results:

• ER8411 connected to WAN via 1 Gb port → speeds are ~900 Mbps+ (download and upload are good)

• ER8411 connected via TL-SM5310-T to the modem’s 2.5 Gb port → download speed capped at ~500 Mbps

• ER8411 connected to MikroTik via TL-SM5220-3M DAC → download speed also capped at ~500 Mbps

• Modem connected directly to a laptop via the 2.5 Gb port → download speed ~1.8 Gbps

Upload speed in all scenarios is ~200 Mbps, which is normal for Rogers in Canada.

I also tried enabling flow control on the router’s WAN SFP+ port, but it made no difference. Download speed remains capped around 500 Mbps.