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SFP+ to SFP not working in a strange way

[ Edited ]

Controller is 4.8.20 (Win32)

 

I have a 48port 500W UniFi switch, and four 16port 250W UniFi switches. Three of which are in other buildings (<400ft) with multimode fiber connections. I desire to connect all four switches via fiber to the 48port.

 

After learning that an SFP module will not work in an SFP+ port, and reading on compatibility for UniFi switches in other threads, I purchased two SFP+ modules and two SFP modules from Ubiquiti. The TrendNet SFP modules I had already owned seem to function without issue when just using SFP is connected to SFP, so the Ubiquiti modules were purchsed after the fact. I set the SFP+ ports to manual/1Gb with the Ubiquiti modules, and put the Ubiquiti SFP modules in the switches on the other end of the connection with the SFP+ SFP+ modules. When using a short 1M cable to connect SFP+ to a SFP test switch, this works. When trying to connect to a switch in another building, no dice. I get lights on the 48port indicating activity, but no lights on the other end and no presence in the controller for the remote switch. If I move the fiber connection from the SFP+ to an SFP port on the 48port, it works. Move it back over to SFP+ port, nothing.

 

Why?

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Re: SFP+ to SFP not working in a strange way

To clarify , SFP gbics work in SFP+ ports, but SFP+ gbics do not work in SFP ports. Additionally, your gbics must match on both ends for both fiber type (MM or Single mode) and sfp type (SFP or SFP+).

In your situation (all downlinks are SFP only), you need SFP gbics on both ends of each link, including in the SFP+ ports on the USW-48.

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Re: SFP+ to SFP not working in a strange way

Tried to find where I read about the compatability of module types to port type and can't find it. Maybe I misread. The only combination I haven't tried yet is SFP module in SFP+ port with manual negotiation set to 1Gbs. I will be able to try Monday. The 10Gbs modules at 1Gbs don't seem to work however.

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Re: SFP+ to SFP not working in a strange way

Just to be cryatal clear these really aren't GBICs - those were older units pre-SFP design.   Not a big deal but there's enough confusion here already.

 

On the SFP/SFP+ issues, think of it this way -  SFP is 1Gb only.   SFP+ is 10Gb.   There are autonegoting units of both but they're rare.   So treat them as only communicating like-to-like, and you'll be pretty safe.

 

SFP+ modules won't work in SFP ports.   SFPs may work in SFP+ ports, but you likely need to set the port speed to 1000Mb manually.   And you're usually best off using modules on both ends from the same vendor (and the same model).

 

If two like modules will talk over a short fiber, but not a longer one, there are several possible causes - the fiber may have too much loss (caused by damage to the fiber or poorly installed or dirty connectors), the optical power may not be enough to get through (there are different Tx power modules available), or it might be the wrong kind of module for the fiber - use single mode modules with single mode fiber and multi-mode with multimode fiber.    In most cases if the correct modules are used with the right type of fiber terminated correctly and at a length within the  specs of the modules, it will just work.

 

Then there's the light wavelength - the two modules have to be matched here also.  

Jim

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Re: SFP+ to SFP not working in a strange way

In most cases, SFP can work on SFP+ port, this depends on your switch type, but SFP+ never work on SFP port. It’s just a power availability thing. When you plug the SFP module in SFP+ port, the speed of this port is 1G not the 10G. And sometimes this port will lock the speed at 1G until you reload the switch or do some fancy set of commands. Besides, the SFP+ port usually can never support speed under 1G. That is to say, we can’t plug the 100BASE SFP in the SFP+ port.
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Re: SFP+ to SFP not working in a strange way

[ Edited ]

TLDR Enable manual negotiation on both ends.

 

I resolved the issue. While this wasn't obvious to me, I fixed this by setting manual 1Gbs negotiation on the other end of the fiber connection as well. It's not enough to set this on the SFP+ port. You have to set this on the switch at the other end as well. So, I have learned that both SFP and SFP+ modules work in SFP+ ports. Didn't try SFP+ modules in SFP ports as I didn't have time. But currently I have Ubiquiti 10Gbs SFP+ modules in their respective ports, communicating with Ubiquiti and TrendNET SFP modules in the receiving switches without issue.

 

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