trying to trace network down (collisions or packet drops)

[MahmoudNassar]

hi experts 

Here's my topology: an HP core Switch 8206zl  and an HP ProCurve switch 2920... We have about 30 Procurve ,aruba each switch connected direct to core switch by fiber

3 Vlans ) Data,Voice , MGM

Only tow switches connected together  cascaded

we don't have any load balancer in the network

 I found some departments has small switch 8port TP Link   ,PCs department connected to this switch and the switch connected to main switch in the floor

All thing is ok

Yesterday we found all the network down for 3 minutes then retuned well as before  

When I check all switch log I found in 5 switch : A large number of collisions or packet drops have occurred on port.

And when check core witch there no log for this issue

Please any one help how to trace this issue to avoid occurs again and what is the reasons for this issue 

thanks 

[Omarrsd]

HI Dear , When your Network was down , that time did you check client were getting proper IP Address? Secondly I suspect there was loop created in your network. check the following things.

Check SPanning Tree In your swithces. As you know Spanning tree is disable by default in HP Switches.

And I have also suspect your switch 8port TP Link Maybe loop was created form there.