I have a network with 3 Cisco SG500.
They are stacked with the S3/S4 ports with fiber in a ring.
So all is working as expected, but when I add a device on switch 2 or 3, I lose connection to switch 1. Like if it reboots and it takes a while (minutes) before coming on-line again - and some times switches 2 and 3 reboot too.
I took switch 3 (28P) out of the stack and now the problem is gone. I reseted that unit and connected it over a standard port to unit 2 and it is working too. So I think there is a problem with stacking or a configuration problem.
What can provoke this behavior?
It's the first time I stack switches so I might have missed something important.
Which ports are you plugging the new devices into? You mentioned you had a ring topology, so I'm assuming the connection goes from Switch 1 > 2 > 3 and then back to 1?
You can also hook up a console cable and take a look at any messages that come up when they reboot. It almost sounds like you are triggering a stack master election.
Do the switches ever get reset, like they would when a new master is elected?
You can also check what firmware is on each switch. The ones that are still stacked can be upgraded together, but the one you removed should be upgraded on it's own and then added back in. Make sure you upgrade the bootcode and set the new active image on each switch as well.
Let me know if any of that helps,
Network Support Engineer - Cisco Small Business Support Center
You're right, the units are configured in a ring topology.
SG500-28 port 27 -> SG500-52 port 51
SG500-52 port 52 -> SG500-28P port 27
SG500-28P port 28 -> SG500-28 port 28
The behavior looks like a master election, rebooting units and loosing all network connections.
Each unit is on the same firmware, 184.108.40.206, boot 1.3.7.01.
I got the Sg500-28P replaced and the same problem occurs, so it might be an other problem or a problem with this specific model?
In the moment, the SG500-28P is in standalone mode to let the rest of the stack work as intended. This unit connect our VoIP phones so I try to avoid playing too much with it during office hours...
I have never seen where there are problems stacking between V1 and V2 hardware.
Do we have any logs from when this happens? Since it looks like they are rebooting logging to an external syslog server would ensure we don't lose the logs at the reboot. It is possible there is some problem with the third switch, since adding that one seems to cause the problem, but since you already replaced it once, I am inclined to agree, it's more likely to be configuration then a hardware issue.
What model of SFP are you using to stack these switches?
I'm using Cisco SFP+ SFP-10G-SR modules. I tried with cheap compatible modules but it changes nothing.
For the logs, I'll have to test again and come back.