Must be a simple VLAN issue, any help appreciated!

Hi there,

I have attached a network diagram to show you how the network is set out.

Everything in the diagram was working until I went to install Managed Switch4 in the diagram. As soon as I connect Managed Switch4 Port8 to Managed Switch3 Port3 we lose connection to the Backup Site and all clients in the Primary Site cannot connect to other devices on the LAN. Strangely as soon as I make the above mentioned connection Cisco ASA A and Cisco ASA B both become Active.

I have configured the network EXACTLY as it is in the diagram. Can you see any problem with my VLANS that would cause the clients in the Primary site to lose LAN connectivity? This all literally happens the second I connect Managed Switch4 Port8 to Managed Switch3 Port3.

I would really appreciate any help, in theory this all looks like it should work fine.

Kind Regards

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NetExpert Network Solutions Pte LtdTechnical SpecialistCommented:
First there is no network diagram attached.

while you connect the new switch ,i suspect, some kind of STP issue occurred on the network,

can you run the below command on the current switch and new switch; would like to know the STP Priority on the new switch

#sh vtp status
#sh spanning-tree
robclarke41Author Commented:
Hi there, sorry diagram attached!
NetExpert Network Solutions Pte LtdTechnical SpecialistCommented:
while  you connect switch 4 to the network, I am sure there is a STP loop is happening on your network.

can you run the below command on switch 2,switch 3 and switch 4

#sh vtp status
#sh spanning-tree vlan 1
#sh spanning-tree vlan 102
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robclarke41Author Commented:
Hi there, YES! I think you are on to something with the STP problem.  I am using HP1910 switches though and only have access to the web interface at the moment.  I could post the STP config page?
NetExpert Network Solutions Pte LtdTechnical SpecialistCommented:
OK.. Please verify and compare the STP configurations (priority,instance etc)between working switch to new switch.

You can take a screenshot of those config and please post it here for further analysis.

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robclarke41Author Commented:
Thank you, I am looking into it now and will post screenshots.
Don JohnstonInstructorCommented:
I would agree that STP is a likely culprit.

Some HP switches have Spanning Tree disabled by default.

Are all the switches in the network HP?  If not and some are Cisco then you will need to change the spanning tree configuration since the default Cisco STP is no compatible with the HP default STP.
robclarke41Author Commented:
Have to give it to Netexpert, was straight in there with the perfect answer in minutes.
robclarke41Author Commented:
Hi There, sorry I think I over-estimated my ability to solve this.  I thought all I would have to do would be enable STP and all would be well.  It turns out that STP was already enabled and making the connection kills the entire network again :(  I've attached screenshots of my STP settings if you wouldn't mind taking a look?
robclarke41Author Commented:
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