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Three cisco 2960 lose connection when I insert a new cisco 2960 in LAN

boldobaldo
Level 1
Level 1
Hello everyone.
I'm trying to practice with cisco 2960.
I want to make a little lan network of four Cisco 2960. 
The first three switches have been configured and are working properly.
When I put the fourth switch in lan, all the other cisco 2960 switches go down.
There's no spanning tree, it's off.
I don't understand which configuration can cause this problem.

 

Thank you all for your help.
7 Replies 7

balaji.bandi
Hall of Fame
Hall of Fame

First check :

 

1. is there any loops in the network

2. Make sure you running VTP in trasparent mode

3. is the 4 switches daisy chain ? not stacked right ?

4. what logs you see on other switches

 

how are you resolving the issue removing 4 th switch, all work as expected ?

 

BB

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How to Ask The Cisco Community for Help

I mistakenly tried to simplify the description of the problem without explaining everything well.

 

Actually, these four switches were inserted into a lan of dozens of other brand switches. (HP)

 

The first three switches work correctly.
I put the fourth in the LAN, and only the cisco switches go down.
All HP don't have any problems.
If I remove the fourth cisco switch, the other three come back up.

 

If there were L2 problems, the hp had to go down as well.

What do you mean "go down"?

 

DO they shut off?

DO you lose connectivity?

Log into the console of one of the switches and see if you can get error logs. Take off configs on Console lines that would prevent you from logging in if the switch was "separated" from the network.

 

-David

 

If there were L2 problems, the hp had to go down as well.

Sure some may have issue, some may not, especially Cisco evil spanning loop and VLAN1 as default vlan

 

we asked what is the Logs you see when this go down, on other switches and also on 4th Switch.

 

any switch by default spanning-tree running, can you post the below information.

 

show version

show vlan

show spanning brief

show logg

 

 

BB

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How to Ask The Cisco Community for Help

if chain topology then It ok no L2 loop

if other topology then sure it is L2 storm.

I mistakenly tried to simplify the description of the problem without explaining everything well.

 

Actually, these four switches were inserted into a lan of dozens of other brand switches. (HP)

 

The first three switches work correctly.
I put the fourth in the LAN, and only the cisco switches go down.
All HP don't have any problems.
If I remove the fourth cisco switch, the other three come back up.

 

If there were L2 problems, the hp had to go down as well.

for HP why it don't down I have little info. about HP SW.
but for Cisco sure it Loop and cisco SW have feature protect SW from L2 Loop or the CPU is high utilize and then SW is down.
you mention that you disable STP why ?