Wrong election of root bridge SG200-18

[riovenitti]

Hi all,

We had recentrly updated our LAN topology with fiber cabling and new switches. We have reused a CISCO SG200-18 switch to serve a zone of our campus and we are happy with it.

Our new topology is based on 2 x Dell N3048 core swiches (named Core1 and Core2) connected one each other and both connected to our CISCO SG200-18 (named Edge5) using a redundant 1Gb link, like this:

Core1 ---------- Edge5

    |                       |

Core2 --------------|

We have enabled RSTP protocol to solve the cycle by electing Core1 as ROOT bridge with the highest priority 8192.

The alternate root bridge is the Core2 with priority set to 16384. All the 5 edge switches are connected to both core switches with default priority 32768.

They are 3 x Dell N2048 (10Gbit fiber link), 1 x CISCO SG300-28 (2Gbit LAG/LACP) and the SG200-18 (1Gbit). All the other switches elected as ROOT bridge for the topology the CORE1 switch as expected.

We have also a Zyxel NWA-1100N wireless AP connected to the SG200 and the switch chooses it as root bridge instead of the CORE1 (even if it has lower priority, 32768). The SG200 seems not to choose the highest priority of CORE1 in any way. Once the Zyxel is connected it's elected as root beacuse switch "senses" the topology change. Now the AP is heavly used and will be free later this afternoon and I will try to disconnect the AP and reboot switch to see what is elected when the AP is not present, and I will let you know.

We cannot connect the redundant link to CORE2 because it will cause a loop. We don't know really how to solve this.

The SG200 has firmware version 1.3.0.62, boot 1.1.0.6 and language en-US 1.3.0.62

Thank you for your help.

Cheers,

Riccardo.

[n0tidgreat]

I'm experiencing the same issue. However on my end, the Network goes like this CoreSw1 and CoreSw2 wherein CoreSW1 is Active and the other one is Standby. Next would be DistributionSW which has connections for both CoreSW and it is a 3750 Switch. Below would be C2960 Access Switch and connected to it is SG200-18 switch. I have checked that from C2960 it has the right STP root which is the Core but upon checking on the SG200-18 it sees it self as the root and/or sometimes it see other SG200-18 switch. And because of this some users was able to get valid IP and then turned to APIPA or for some point totally APIPA. i have attached one SG200-18 STP status.

Help please!!!

[riovenitti · Accepted solution]

Well, I've checked and double-checked and found the problem. There problem was that the colleague that put the cable used inadvertently the wrong port. The wrong port was set in port-fast mode and thus it was not elegible for root path. I reconnected everything as it should be and now it works flawlessly.

So perhaps this could be the same problem for you.

Cheers

[n0tidgreat]

I see. However, on my end I think that's not the case. config of C2960 switch where it is connected is just trunk port and assigning vlan 100 as native. Do you have any other idea? what is you current firmware?