2960 switch down

[jai.s401]

The L2 switch went down i.e all the end users had disconnected from the network, No network symbol.

After 5 minutes plugging and unplugging the uplink port the network came Up.

Don't know if it came up because of unplug and plugging uplink

and found only the below logs :

Syslog logging: enabled (0 messages dropped, 1 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)

No Active Message Discriminator.

No Inactive Message Discriminator.

Console logging: level debugging, 5020 messages logged, xml disabled,
filtering disabled
Monitor logging: level debugging, 0 messages logged, xml disabled,
filtering disabled
Buffer logging: level debugging, 5020 messages logged, xml disabled,
filtering disabled
Exception Logging: size (4096 bytes)
Count and timestamp logging messages: disabled
File logging: disabled
Persistent logging: disabled

No active filter modules.

Trap logging: level informational, 5022 message lines logged
Logging Source-Interface: VRF Name:

Log Buffer (4096 bytes):
down
May 17 18:24:20.907: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed st ate to up
May 17 18:24:21.956: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, chan ged state to up
May 17 18:24:22.917: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet1/0/48, changed state to up
May 17 18:29:10.052: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, chan ged state to down
May 17 18:29:11.010: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet1/0/48, changed state to down
May 17 18:29:12.013: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed st ate to down
May 17 18:29:15.253: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed st ate to up
May 17 18:29:16.340: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, chan ged state to up
May 17 18:29:17.263: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet1/0/48, changed state to up
May 17 18:29:31.778: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, chan ged state to down
May 17 18:29:32.740: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet1/0/48, changed state to down
May 17 18:29:33.743: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed st ate to down
May 17 18:29:39.503: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed st ate to up
May 17 18:29:41.418: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, chan ged state to up
May 17 18:29:41.513: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet1/0/48, changed state to up
May 17 18:29:45.221: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, chan ged state to down
May 17 18:29:46.179: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet1/0/48, changed state to down
May 17 18:29:47.186: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed st ate to down
May 17 18:29:53.861: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed st ate to up
May 17 18:29:55.504: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, chan ged state to up
May 17 18:29:55.871: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet1/0/48, changed state to up
May 17 18:30:07.724: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down
May 17 18:30:08.699: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/48, changed state to down
May 17 18:30:09.705: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to down
May 17 18:30:28.461: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to up
May 17 18:30:31.023: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to down
May 17 18:30:39.101: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to up
May 17 18:30:41.110: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/48, changed state to up
May 17 18:30:41.823: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up
May 17 18:30:51.299: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down
May 17 18:30:52.260: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/48, changed state to down
May 17 18:30:53.267: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to down
May 17 18:30:56.619: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to up
May 17 18:30:57.922: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up
May 17 18:30:58.632: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/48, changed state to up
May 17 18:31:08.366: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down
May 17 18:31:09.341: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/48, changed state to down
May 17 18:31:10.348: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to down
May 17 18:31:13.585: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/48, changed state to up
May 17 18:31:14.686: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up
May 17 18:31:15.598: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/48, changed state to up

48th port is the trunk port to core switch.

cleared the interface counters and checked after that no CRC error Occured after that.

why the Interface vlan goes down ?

How can i troubleshoot this ?

How can i find route cause of this issue and prevent it from happening in future.

[jai.s401]

Hi Leo,

Thanks for the reply. I have few questions here.

FCS error what it indicates.

layer 1 issue ? means with the cable or the Lan port ?

layer 1 in OSI layer or TCP/IP layer?

[MHM Cisco World]

there are huge number of broadcast and multicast, 
there was I think L2 storm and by plug and unplug the uplink you stop L2 storm and hence the UPLINK return to work.
do you config any storm control?  check this log in Core/Agg SW

%STORM_CONTROL-3-FILTERED: A Broadcast storm detected on Fa0/5. A packet filter action has been applied on the interface.

[jai.s401]

well that might be the case because we have configured Port-fast in most of the ports but the end user confirmed that they have not connected anything other than host to those ports.

for the storm control query, it is No, we have not configured anything manually on that part.

[MHM Cisco World]

port-fast must not config in any port interconnect two SW, but if the port-fast config it can cause temporally storm.
in case you config port-fast and you want to protect the port then BPDU guard can config with port-fast to make port go to err-disable before the storm effect your network.

[MHM Cisco World]

gi1/0/48 what is the VLAN assign for this port ?
do show spanning tree vlan 

Number of transitions to forwarding state: 0 <- this is it must not increment or at least low number compare to other port