all switch port down in few second when i try to "no shutdown" 1 port

[hungvu.bk37]

Hi All,

When I try to open 1 port by "no shutdown" command, all another port is down in few second and automatic up after that.

Anyone know why I got this issue?

Thank you so much.

[Leo Laohoo]

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@hungvu.bk37 wrote:

When I try to open 1 port by "no shutdown" command, all another port is down in few second and automatic up after that.

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BPDU Guard kicks in and someone has enabled auto-recovery.

[hungvu.bk37]

the port I enable no BPDU config

[Leo Laohoo]

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@hungvu.bk37 wrote:

the port I enable no BPDU config

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The config provide is incomplete for me to change my mind.

[marce1000]

- Check logs on your switch when that happens.
M.

[David Ruess]

Hello,

What's connected to that 1 port. It could be spanning tree doing a recalculation and temporarily blacing ports in blocking mode.

Can you provide a diagram and config of the devices you are working with?

-David

[hungvu.bk37]

this port just connect to a device

[MHM Cisco World]

there is STP loop, no shut make port recover from err-disable it was in,
so
before no shut
do show inteface status 
check if the port in err-disable status, 
if yes then check if the port connect to SW and not to host
if it connect to SW then check STP config 
the port must not be portfast
the port must not be BPDU guard.

[hungvu.bk37]

this port I enable just connec to a device, no portfast, no BPDU guard

[MHM Cisco World]

in port you connect this device and make all port to shut down, 
please config below command 
then try again.
switchport block unicast

[hungvu.bk37]

I attached the switch configuration 

[Seb Rupik]

Hi there,

You have disabled portfast on all of the switchports, this means they are designated as non-edge ports via RSTP. Whenever a non-edge port starts forwarding (ie you connect gi0/1) a topology change is generated. This causes the switch to clear its MAC table and send out BPDUs to connected switch notifying them of the topology change and to perform the same MAC table flush. This will ripple across the entire network.

I don't believe the switchports get shutdown, but there will be a perceivable loss in communication on the switchports.

Is there a good reason why you have disabled portfast on your access switchports?

cheers,

Seb.