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[Alex Atkin UK]

I've re-built my server over the last couple of weeks to a spanking new i5 12400 with 8x drive bays and a SAS controller.

Naturally as part of this I had to do a lot of dust clean up from the shelf the server was on, tidy up the cables, and unfortunately no longer use DAC as I can't find the full height bracket for my card.    Fortunately I have an AQC107 knocking around that was constantly cutting out on Windows, but seems to work perfectly fine on Linux (touch wood).

Anyway, the point of this is I was tidying up the UPS, removing a 4 gang adapter I no longer need so everything plugs straight into the UPS.  This meant powering down my Netgear MS510TXUP for a while as that was the only thing left in the adapter.  However, when I powered it back up, I couldn't get into the WebUI to change the names of the ports I had now reassigned duties - which I use as I pull statistics off it via SNMP including the name of the device plugged in.  It was, however, responding to pings.  Curious.

So I powered cycled it a second time and now, no ping, its not showing on the network at all - oh crap.

On a whim I tried unplugged the things I had swapped over and it briefly worked then dropped off the network again.  Upon checking everything else, I pushed the SFP+ adapter linked to my second switch and heard a click - aha.  Seems I had slightly pulled it loose when I unplugged the DAC.  Everything magically working again.

The curious thing through all this is packet switching and PoE remained functional the whole time, though in hindsight my other PC connected to the switch linked over that SFP+ port HAD lost connectivity, but the port on the switch still said it had a link.

The PC I was trying to access the switch UI from however was NOT connected to that second switch, it was directly to the main one.  So, somehow, the SFP+ not being plugged in correctly killed the networking on the switch, but had no impact on the switching.  What a weird failure mode.

[burakkucat]

Hmm . . . An odd state of affairs. 

However I will mention that SFP (& all other types of small form-factor pluggable) interfaces have different lengths to the gold-plated contacts of the edge connector to ensure that certain contacts are made before others, when hot-plugging in, and the converse, when hot unplugging.

[Alex Atkin UK]

Yeah I think most connector make sure ground is connected first, or at the same time as voltage - data lines are last.

[burakkucat]

<Nods.>

[Alex Atkin UK]

I don't know if its been working loose over time as I swear the whole network seems more responsive than before.  I'm kinda wondering if my Intel X520-DA1 was slowing down the switch somehow. :/  I did used to get retries doing iperf3 which niggled at me, none at all now and much more consistent speed result.

[burakkucat]

I forget. Did you purchase the Intel X520-DA1 new or was it a second-hand bargain?

I have a vague memory that someone else purchased similar around the same time you. Possibly Ronski.

[Alex Atkin UK]

I believe it was brand new.