Hello,
I was thinking of purchasing RB5009UG+S+IN to upgrade my home network to 2.5G capability, but I have read some worrying things that there is some issue that could prevent me from utilizing full speed. My ISP is soon upgrading their hardware and providing 2.5G internet speed.

I would like to connect 2.5G copper Eth port from ISP GPON ONT to RB5009 2.5G Eth port. Some 1G clients (WLAN ap, printer...) would also be connected to this router. Then RB5009 10G optical fiber connection to some switch (haven't decided yet) and to the switch I would connect my PC 2.5G LAN.

Would I be getting full 2.5G speed with this setup or is there still some bug/feature with the switch chip that prevents it? I haven't fully understood the issue so I'm hoping someone could clarify this for me. Thank you!

I would not use the Switch ports on the RB5009. Use the 10Gig Uplink to a switch that supports 2.5 like
https://mikrotik.com/product/crs326_4c_ ... ifications
or
https://mikrotik.com/product/crs310_8g_ ... ifications

I would not use the Switch ports on the RB5009. Use the 10Gig Uplink to a switch that supports 2.5 like
https://mikrotik.com/product/crs326_4c_ ... ifications
or
https://mikrotik.com/product/crs310_8g_ ... ifications

Thanks for the reply. Using the 10G uplink to a 2.5G switch is what I'm planning to do. But how would you suggest connecting the ISP GPON to this setup?

I would not use the Switch ports on the RB5009. Use the 10Gig Uplink to a switch that supports 2.5 like
https://mikrotik.com/product/crs326_4c_ ... ifications
or
https://mikrotik.com/product/crs310_8g_ ... ifications

Thanks for the reply. Using the 10G uplink to a 2.5G switch is what I'm planning to do. But how would you suggest connecting the ISP GPON to this setup?

You got it right.

Wan in the 2.5 ether 1.
Switch connected to 10Gig SFP+ port.

Router only routes. No other connections to router (aside from power).

I would like to connect 2.5G copper Eth port from ISP GPON ONT to RB5009 2.5G Eth port. Some 1G clients (WLAN ap, printer...) would also be connected to this router. Then RB5009 10G optical fiber connection to some switch (haven't decided yet) and to the switch I would connect my PC 2.5G LAN.

It should work, no problems. I just got one RB5009, but haven't the time to thinker with it yet. I'm about to test 2,5Gb too - but it's not set up yet.

What I can say about it:

1) Take a look at the block diagram (https://i.mt.lv/cdn/product_files/RB5009UGS_220852.png). All 10 ports are connected to the same switch chip - and it's non blocking. We can carve them out as we want, but in hardware terms, one can get full switch speed on all ports, and full duplex 10Gb/s to/from CPU.
2) Take a look at the test results (https://mikrotik.com/product/rb5009ug_s ... estresults). To get real world worst scenarios I consider the "Routing, 25 ip filter rules, 512 byte" speed - its 3096Mb/s. But this is with a complex setup, and without using fast path. With fastpath... well, it hits 9551Mb/s.
3) "But how fast can it go?". Well, I had one hEX750Gr3. By this table it should do 1820 Mb/s with fast path and 385 Mb/s on the heavy scenario. Mine saturated a one gigabit link - with PPPoE. Well, almost: it made 925Mb/s. I think that's was due to the PPPoE overhead.

So. "Should it work, and deliver the speed I need?" Oh, yes. One would be hard pressed to mess up this bad the config.
Will your connection layout work? Yes, it will. At least it should. There is nothing wrong with it.

About your question on "how would I connect all this through only the SFP+ port?" Take a look on "router on a stick". I don't recommend, as it adds complexity - but it's doable.

Thanks for the reply. Using the 10G uplink to a 2.5G switch is what I'm planning to do. But how would you suggest connecting the ISP GPON to this setup?

You got it right.

Wan in the 2.5 ether 1.
Switch connected to 10Gig SFP+ port.

Router only routes. No other connections to router (aside from power).

I've been trying to troubleshoot this on my RB5009 as well. Currently I have my ISP connected to the 2.5G Port and the 10SFP+ to my Switch. Unable to reach the correct speeds.
If you have any insight that would help. I've tried swapping the connections around and it seems my speed caps out at 1400mb/s

Thanks for the replies. I know reading the tech specs that it should have no problem getting 2.5G speeds, but I keep reading posts like Viability6655 so I am still uncertain about my purchase.