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colonelbeefies
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Speed Test over 40Gbps QSFP28 link slow

Fri Jan 27, 2023 12:31 am

I've got two CRS518-16XS-2XQ switches. I've added a FS QSFP-LX4-40G (QSFP+ fibre) transceiver to each and connected them up with a 2m OM3 patch lead for testing. Auto negotiation wouldn't work, but setting them to 40G full duplex worked. I've assigned an IP address to each interface. I've set the FEC Mode to fec91 as that gives me 0% packet loss.
The SFP tab says that the SM Link Length is 2.000km. I think that might be hard coded into the SFP module though.

I've run a speed test between the two and I currently get 178Mbps up and down on UDP with the CPU load maxing out at 100% with 0% packet loss. The speed worries me as that's far lower than the 40Gbps I'm expecting.

Is this expected behaviour, or is that a bit lower than expected?

I want to setup a PC bandwidth test between the two, but I don't have any SFP28 enabled servers at the moment.

EDIT: Forgot to mention both switches are running routeros 7.7
 
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chechito
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Re: Speed Test over 40Gbps QSFP28 link slow

Fri Jan 27, 2023 1:35 am

bandwidth test run using CPU

switches have an small CPU only for management

for testing 40g you will need several servers on each end of the link to generate traffic
 
colonelbeefies
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Re: Speed Test over 40Gbps QSFP28 link slow

Fri Jan 27, 2023 3:29 am

I see the CPU is QCA9531, 1 Core, 650MHz, 64MB RAM. I shouldn't be worried about these results?
I did notice that when I exported the config the CPU went to 100% for a few seconds.
 
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chechito
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Re: Speed Test over 40Gbps QSFP28 link slow

Fri Jan 27, 2023 4:33 am

https://help.mikrotik.com/docs/display/ ... width+Test
Bandwidth Test uses a lot of resources. If you want to test real throughput of a router, you should run bandwidth test through the tested router not from or to it. To do this you need at least 3 routers connected in chain: the Bandwidth Server, the router being tested and the Bandwidth Client.

in your case you need 4 devices, your 2 switches connected by 40g, plus 2 servers/routers with 4 x 10 g ethernet interfaces on each server/router for each end of the test and enough CPU power to push the test-traffic on that servers/routers

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