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dpscisco
Beginner

Problem with sg500 ports blocked by STP

We have a Switch SG500-52P connected to a 2960x using a Single Mode fiber through the port g1/1/49, and also it is connected to two other SG500 switch through the ports G1/1/19 and G1/1/36 respectively. by copper links. There is no redundant links implemented into the switches mentioned. The Switches are also configured with RSTP.

 

Lately, every 10 or 15 minutes the network is being interrupted constantly. Into the SG500 appears logs that mention that the ports G1/1/19 and  G1/1/36 are suddenly blocked and after few seconds are into forwarding state. At the same time, into the 2960X switch side there are logs indicating that the fiber link gets down and later gets up after few seconds.

 

13:01:14 :%STP-W-PORTSTATUS: gi1/1/36: STP status Forwarding

25-May-2021 13:01:14 :%STP-W-PORTSTATUS: gi1/1/36: STP status Blocking

25-May-2021 13:01:14 :%STP-W-PORTSTATUS: gi1/1/19: STP status Blocking

25-May-2021 11:16:59 :%STP-W-PORTSTATUS: gi1/1/19: STP status Forwarding

25-May-2021 11:16:59 :%STP-W-PORTSTATUS: gi1/1/36: STP status Forwarding

25-May-2021 11:16:59 :%STP-W-PORTSTATUS: gi1/1/36: STP status Blocking

25-May-2021 11:16:59 :%STP-W-PORTSTATUS: gi1/1/19: STP status Blocking

 

 

May 27 08:52:02: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/2, changed state to down
May 27 08:52:03: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/2, changed state to down
May 27 08:52:06: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/2, changed state to up
May 27 08:52:08: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/2, changed state to up

 

I am not able to find flapping events or duplicated MAC Addresses. I am not able to find the cause of the interruptions or the blocked ports.

1 REPLY 1
marce1000
VIP Advisor

 

 >...I am not able to find flapping events or duplicated MAC Addresses. I am not able to find the cause of the interruptions or the blocked

  - Use a syslog-server for all involved cisco devices, you may (sometimes) have a loop indeed, usually when the logs are collected centrally you will get an overview of looping-syndromes (or other issues) , if any. The then displayed mac addresses may then point to the cause of the loop.

 M.