Network Outage and where to look for problem???

[q-le]

Hi All,

We have network outage yesterday where most of our users suddenly lost network connection and after a couple of minutes the network let them

log back in.

We have a dual Core Nexus 7k , hundreds 3750 access switches of mix 3750x and olders 3750G and hundred of  Air-CAP3502Wifi APs

We have Solarwind in place but after checking the Cores , Solarwind and Switches ' logs  -  We see nothing wrong.

Just wondering what could go wrong here and where do we begin to troubleshooting or where to look for errors?

Any suggestions are much appreciated.

Thanks

Peter

[Suresh Vinayagam Subramanian · Accepted solution]

Hi,

You can check below things.

1. Narrow down the problem like : is all the users are affected or one segment/floor/vlan or users only connected to few switches?

2. once you identify above this than check the logs on those switches.

3. If all the users are affected than we have to move to core switch otherwise issue could be in access switches.

4. check the logs to see if we get any STP loop or hsrp flap.

5. Also check the switch CPU and interface utilization details.

HTH
Regards,
VS.Suresh.
*Plz rate the usefull posts *

[q-le]

Hi Suresh,

Thank you very much for the response.

How do I check for HSRP flap or STP loop? 

These are the areas that i am not familiar with .

Peter

[Suresh Vinayagam Subramanian]

Hi,

Primary place is " show log " on each device. Also you can use below commands.

show spanning-tree detail   ---> see how frequent topology changed and from which interface last TCN received.

show standby brief

also you can enable " mac-address-table notification mac-move" command on switches. so that it will show you if there is any stp issue or mac moves on the switch. 

HTH
Regards,
VS.Suresh.
*Plz rate the usefull posts *