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Hi!

We have a spanning tree that gets bigger and bigger and a loop problem with STP.
About once a day a loop appears that kills the network and wedges some routers. It lasts for a few minutes and everything comes back to normal.

While looking at the logs to try to understand, we found something odd.

The root of our spanning tree is a mikrotik switch connected by two fibers to two WS-12-250-DC and WS-12-DC.

On those switches when the network goes crazy we have those kind of logs :

The ports 1 and 5 are Stp enabled ports to the inner network.
Port 13 is a Stp enabled backup fiber link to the other top switch.
Port 14 is a Stp enabled fiber link to the root and uplink.

Code: Select all

 Dec 25 16:30:24 STP: set port 26 to discarding
Dec 25 16:30:24 STP: set port 25 to learning
Dec 25 16:30:24 STP: set port 25 to forwarding
Dec 25 16:30:25 STP: set port 1 to discarding
Dec 25 16:30:26 STP: set port 26 to learning
Dec 25 16:30:27 STP: set port 26 to forwarding
Dec 25 16:30:28 STP: set port 25 to discarding
Dec 25 16:30:29 STP: set port 5 to discarding
Dec 25 16:30:29 STP: set port 1 to learning
Dec 25 16:30:29 STP: set port 1 to forwarding
Dec 25 16:30:30 STP: set port 25 to learning
Dec 25 16:30:31 STP: set port 25 to forwarding
Dec 25 16:30:43 STP: set port 5 to learning
Dec 25 16:30:43 STP: set port 5 to forwarding
Dec 25 16:30:44 STP: set port 1 to discarding
Dec 25 16:30:45 STP: set port 1 to learning
Dec 25 16:30:46 STP: set port 1 to discarding
Dec 25 16:30:47 STP: set port 1 to learning
Dec 25 16:30:48 STP: set port 1 to discarding
Dec 25 16:30:59 STP: set port 1 to learning
Dec 25 16:30:59 STP: set port 1 to forwarding
Dec 25 16:30:59 STP: set port 5 to discarding
Dec 25 16:32:05 STP: set port 5 to learning
Dec 25 16:32:05 STP: set port 5 to forwarding
Dec 25 16:32:05 STP: set port 5 to discarding
Dec 25 16:32:07 STP: set port 1 to discarding
Dec 25 16:32:07 STP: set port 5 to learning
Dec 25 16:32:07 STP: set port 5 to forwarding
Dec 25 16:32:07 STP: set port 5 to discarding
Dec 25 16:32:07 STP: set port 1 to learning
Dec 25 16:32:07 STP: set port 1 to forwarding
Dec 25 16:33:49 kernel: link state changed to 'up' on port 26
Dec 25 16:33:49 kernel: link state changed to 'up' on port 26
Dec 25 16:33:49 STP: set port 26 to discarding
Dec 25 16:33:49 STP: set port 26 to discarding
Dec 25 16:33:49 STP: set port 5 to learning
Dec 25 16:33:49 STP: set port 5 to forwarding
Dec 25 16:33:49 STP: set port 1 to discarding
Dec 25 16:33:52 STP: set port 1 to learning
Dec 25 16:33:52 STP: set port 1 to forwarding
Dec 25 16:33:52 STP: set port 5 to discarding
Dec 25 16:33:55 STP: set port 26 to learning
Dec 25 16:33:55 STP: set port 26 to forwarding
Dec 25 16:35:27 pinger: Failure pinging 172.17.0.155, powering off port 7 for 10 seconds
Dec 25 16:35:35 STP: set port 26 to discarding
Dec 25 16:35:35 kernel: link state changed to 'down' on port 26
Dec 25 16:35:35 STP: set port 5 to learning
Dec 25 16:35:35 STP: set port 5 to forwarding
Dec 25 16:35:35 STP: set port 1 to discarding
Dec 25 16:35:36 kernel: link state changed to 'up' on port 26
Dec 25 16:35:36 STP: set port 26 to discarding
Dec 25 16:35:37 STP: set port 1 to learning
Dec 25 16:35:37 STP: set port 1 to forwarding
Dec 25 16:35:37 STP: set port 5 to discarding
Dec 25 16:35:38 STP: set port 26 to learning
Dec 25 16:35:38 STP: set port 26 to forwarding
Dec 25 16:35:38 STP: set port 1 to discarding
Dec 25 16:35:38 STP: set port 25 to discarding
Dec 25 16:35:38 STP: set port 25 to learning
Dec 25 16:35:38 STP: set port 25 to forwarding
Dec 25 16:35:38 STP: set port 25 to discarding
Dec 25 16:35:38 STP: set port 1 to learning
Dec 25 16:35:38 STP: set port 1 to forwarding
Dec 25 16:35:38 STP: set port 5 to learning
Dec 25 16:35:38 STP: set port 5 to forwarding

So I guess that port 25 and 26 are the 13 and 14. But is it normal?

Port 25 = Port 13
Port 26 = Port 14
On the WS-12-250A, WS-12-250B, WS-12-250-AC, WS-12-250-DC, WS-12-DC, WS-12-400AC

Port 25 = Port 9
Port 26 = Port 10
On the WS-10-250-AC

We have discussed this several times that the switch core is the same between all models and the SFP ports are always ports 25 and 26 internally as seen in the log we just show them as 13 and 14 in the UI.

Could you please let us know what firmware version you are using.

Thanks for the very quick reply!

Ok that makes sense.

Both switches are on 1.3.9rc7

So if I understand well, since the the ports 13 or 14 go down first almost all the times, we should start looking at a problem between the mikrotik switch and those two...