S3300-52X-PoE+ Change SFP+ port speeds to go into regular SFP

[danieli-nello]

We have a secondary switch (GS728TPV2) that we would like to connect to our primary switch (S3300-52X-PoE+) through SFP but are running into issues with what I believe to be the differences in speed. I was hoping to be able to downgrade the connection from the S3300 to regular SFP through the IP interface but get an error every time I try to apply the change.

I have tried to set it to the specific speed I want as well as just everything to Auto, but still do not get a connection (and sometimes receive an error stating it could not apply).

Any help would be appreciated, thank you.

[schumaku]

Using fiber modules? Please understand that fiber does not know anything similar to the automatic link speed negotiation we know from RJ45 copper ports on 10GbE, 1 GbE and Fast Ethernet. It's the fiber module defining the link speed. To establish a GbE fiber link between a switch port with SFP+ and a switch with an SFP port, you need the same spec'ed fiber link modules.

[danieli-nello]

When you say modules, are you talking about the physical modules with in the switches?

I am using a Netgear AXC761-1000S cable. From my reading, I have to use a cable that has an SFP transceiver on one end, and an SFP+ transceiver on the other to make the connection.

[schumaku]

The Netgear AXC761-1000S cable is a pure passive 1m long SFP+ Direct Attach Cable. With both ends plugged into a compatible SFP+ 10G port, a 10 Gigabit link speed is expected in both directions.

Not sure on how I should understand the problem description - this is possibly what you would expect between the  S3300-52X-PoE and the other GS728TPV2 switch?

The only thing coming into my mind is that not all SFP+ devices can be operated on such SFP+ DAC connections.

Just for my curiosity, the SFP+ port in the S3300 is configured as a general use Ethernet, not as a stacking port?

[danieli-nello]

I was hoping the transceivers on the Netgear cable would be able to transmit at both 1 G and 10 G, in the same way that RJ45 can transmit at both 1 G or 100 MB. This appears to not be the case, so I will get a custom cable with with transmitters capable of this.

[schumaku]

Afraid, this won't be possible neither with the all passive SFP+ cable (obvious, think about it) nor with SFP+ fiber modules (no speed auto negotiation!). 

The only media knowing about auto speed negotiation would be plain copper Ethernet modules.

[danieli-nello]

I understand there is no auto negotiation in the cable or transceivers, but can this not be set within the switch itself? You are able to choose the speed, duplex, and toggle auto negotiation for other ports, but not SFP?

[schumaku]

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@danieli-nello wrote:

You are able to choose the speed, duplex, and toggle auto negotiation for other ports, but not SFP?

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Correct. 

[danieli-nello]

Unfortunate.

Thank you for your help! I suppose the best solution is to simply get another SFP+ switch then.

[schumaku]

Two AGM731F or AGM732F SFP modules and a matching fiber patch should do the job. Sorry, my bad - missed that the GS728TPv2 does come with plain SFP only.

[danieli-nello]

Oh I think I understand, you are saying I could get the 1 G connection by simply having a regular SFP module on both ends, and the port itself can downgrade?

[schumaku]

Yes, this makes a workable 1G fiber link, also on the S3300 SFP+ port.

[danieli-nello]

Fantastic, thanks again!

[schumaku]

A much more affordable solution using SFP fiber modules from the free market 8-)

[danieli-nello]

Yep, already looking on https://www.fs.com/ they seem to have what I need.