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September 14th, 2025 15:07
What kind of fiber do I need for SFP28 SR Optic, 25GbE, 85C
I'm new to fiber optics. We have a new server equipped with a Broadcom 57414 Dual Port 10/25GbE SFP28, OCP NIC 3.0 and we received two SFP28 SR Optic, 25GbE, 85C with it; one plugged into the server and the other into the switch - a Cisco CBS 350. There doesn't seem to be a manual for those transceivers - I couldn't fine one. So I wonder - what kind of fiber do I need? I already bought a couple of multimode OM4 fibers, but they don't seem to work. Or maybe there's something else I'm doing wrong?
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Origin3k
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September 15th, 2025 08:02
When only dealing with 1.5m you can choose what ever you want ;) Stay on OM4.
The Cisco SFP-10G-SR sounds right because SR means "ShortRange" which is MMF(MultiModeFiber). The LR is LongRange and SMF(SingeModeFiber).
I dont know what the -S in Cisco SFP-10G-LR-S is good for.
BUT having a 10/25G NIC is great these days... but when having a 25G Tranceiver on one site you need another one on the other(and a 25G Switch of course). Dell also have 10/25G Transceivers but iam unsure what exactly do you have bought.
Within the Dell OSC/Shop you can click the 10/25G NIC and dedicated 10G SR Transceivers.
Regards,
Joerg
Origin3k
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September 15th, 2025 08:48
Than just buy the Cisco Tranceiver which is cheaper (HaHaHa) and better available at your current location.
The broadcom NIC supports auto negotiation but you can downgrade it within the Systemsetup if needed.
Regards,
Joerg
YashSmith
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September 15th, 2025 09:10
For a 25GbE SFP28 SR optic rated at 85°C, you need multimode fiber (MMF) with OM4 or OM5 specification. Key points:
Connector type: LC duplex
Fiber type: 50/125 µm multimode
Distance: Up to ~100 m on OM4, slightly longer on OM5
Cable rating: Ensure it’s rated for high temperatures if operating near 85°C environments
At dev technosys, we recommend using factory-terminated OM4/OM5 patch cables or pre-tested trunk cables to ensure optimal 25GbE SR performance.
Origin3k
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September 15th, 2025 05:50
That depends on the length.... but OM4 is cheap support more lenght as OM3 and thats why its comman use. The reason why it not work is that i have my doubt that a Dell 25G transceiver works in your Cisco Switch.
There maybe rare circumstances where you swap the connector on one side of your patch cable.
Regards,
Joerg
Simon Weel
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September 15th, 2025 07:53
@Origin3k The length of the cable is 1,5 meters. I checked the Cisco manual. There's a number of modules the CBS 350 supports:
Which one do I need, besides the Base-T one; the Cisco site doesn't explain the differences...
Simon Weel
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September 15th, 2025 08:17
@Origin3k That's another problem - Dell doesn't tell much about the transceiver in question. But the salesperson told me it supports 10 Gbit as well....
Origin3k
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September 15th, 2025 08:31
Yes... i have in mind. that the 85C are supporting 10 and 25G.
Regards,
Joerg
Simon Weel
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September 15th, 2025 08:32
Copilot to the rescue:
To talk to a 25GbE SFP28 SR Optic, you need a 10G transceiver that uses 850nm wavelength over multimode fiber (MMF) and supports 10GBASE-SR. That means:
Why Choose S-Class?
Ideal for standard data center deployments
Great for short-range multimode fiber links (like SFP-10G-SR-S)
Saves money if you don’t need advanced features like Fibre Channel over Ethernet (FCoE) or Optical Transport Network (OTN)
So if you're just running 10G Ethernet over OM3/OM4 fiber in a controlled environment, S-Class is often the smart choice. Want help picking between S-Class and non-S-Class for your setup?
Origin3k
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September 15th, 2025 09:28
He only has 10G on the other side.
Simon Weel
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September 15th, 2025 09:36
Just ordered a couple of Cisco SFP-10G-SR modules, so we'll see in a couple of days.
Thanks all for helping me out!
Origin3k
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September 15th, 2025 10:17
Your welcome.
Some backupground. The major Network vendors do a whitelisting on Switch site so you cant use a different brand for the optic.
Yes...
Regards,
Joerg