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Diffuse troubles in HP Procurve 4208vl + 3500yl Network

wsa-nick
Occasional Visitor

Diffuse troubles in HP Procurve 4208vl + 3500yl Network

Hello Guys,

 

I've got diffusing network problems in my LAN + SAN / HP Network. You can see my enviromnent in the attached pdf-file.

 

Description to the diagram:

We created on iswitch1 (3500yl) + iswitch2 (3500yl) a second VLAN / LAN1 (all VLAN's in our enviromnent are port-based and with untagged ports config). These two LAN1-VLANs we connected with one cable per unit to our core switch1 (4200vl series). After these connections had been established, the network-problems occured. Stacking on all switches is deactivated, Spanning-Tree is active for our port security appliance.

 

Problem 1)

Devices in SAN1-VLAN on iswitch1 can't see devices on SAN1-VLAN on iswitch3 anymore.

Problem 2)

Also Devices in SAN2-VLAN on iswitch2 can't see devices on SAN2-VLAN on iswitch3 anymore.

 

When we plug out the two cables from switch1 to iswitch1 + iswitch2, the problems are extinct. But thats no option, we need the two VLANs on iswitch1+ iswitch2 witch connection to switch1. Where i have to search the problem? I'm sorry to say, that i've sadly only newbie-knowledge about vlan's and switches.

 

With many thanks in advance for your answer(s). :-)

 

Regards from Germany / EU,

Nick

3 REPLIES
Richard Brodie_1
Honored Contributor

Re: Diffuse troubles in HP Procurve 4208vl + 3500yl Network

I would guess it is spanning tree that is disabling the connections. If your core switch is root, then it's likely that the blue and green links are the ones that end up blocking.

 

"show span" on the switches would tell you. Or you could look at the switch logs, if you didn't want to repeat the experiment.

wsa-nick
Occasional Visitor

Re: Diffuse troubles in HP Procurve 4208vl + 3500yl Network

Richard, thanks for your answer!  :-)

 

According to your consideration, i was experimenting with spanning tree on friday. I created a small test environment like the productive one. In the test-env. i could reproduce the problem. And in fact, after disabling spanning tree on iswitch1 + iswitch2 the problems were no longer. But what i can't comprehend is, why these problems are emerging generally?! I can't locate any logical loop in my environment?

 

For me there is only a physical loop, but it could doesn't matter because of the logical isolation in seperate vlan's. Generally, which disadvantages i'll get when i disable spanning tree on this two switches? With our partner for the port-security unit, I'll consulate if disabling spanning-tree will disrupt the appliance.

 

The command "show span" i'll execute tomorrow on CLI.

 

Once again, thank you very much for your answers. Have a nice sunday!

 

Greetings,

Nick 

 

Richard Brodie_1
Honored Contributor

Re: Diffuse troubles in HP Procurve 4208vl + 3500yl Network

The problem is that the spanning tree layer is between the physical and logical layers. First the spanning tree prunes redundant links, then any VLAN filtering is applied afterwards.

 

You could do it the other way, and computer a separate spanning tree for each VLAN. This is how Cisco's PVST works. However, each switch might have to compute hundreds of different spanning trees, and send very many packets on links with many VLANs present.

 

With MSTP you can have multiple trees active, and links active in one tree but not in another. The configuration needs to be designed rather carefully - it's more efficient than PVST but not at all plug and play.

 

As well as globally disabling spanning tree, you could disable it on selected ports with "bpdu-filter". Or you could go the other way and set up an MSTP region...