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VLAN Trunking & STP question

Posted on 2011-10-21
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Last Modified: 2012-08-13
Currently I'm working with two procurve 5406zl switches.

I have a trunk setup from switch A to switch B that all VLANS are setup on. My boss wants me to create another trunk and just have VOIP traffic on it. At first, without thinking, I thought that would be no big deal but I soon realized that STP considers the second trunk a redunant connection and blocks the connection. Is it possible to have two trunk connections between the two switches and just have 1 VLAN on one trunk and the rest on the other?
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Question by:Iamdriver38
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LVL 17

Expert Comment

by:rochey2009
ID: 37007304
yes this is possible. There are two ways you can achieve this.

on trunk 1 remove the voice vlan from the trunk "switchport trunk allowed vlan remove x"

on trunk 2 allow only the voice vlan "switchport trunk allowed vlan x"

alternatively, you can leave all vlans on both trunks but modify spanning tree for vlan x so that the alternate link is forwarding for the voice vlan.
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Expert Comment

by:Don Johnston
ID: 37008375
If it's just VoIP traffic, isn't that on a single VLAN? If so, you don't need a trunk at all. Just an access link for that VLAN.
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Expert Comment

by:rochey2009
ID: 37008533
or switchport voice vlan if you want to keep the layer 2 cos information
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LVL 17

Expert Comment

by:rochey2009
ID: 37008585
access port, voice vlan (voice vlan is a special trunk) or second trunk; whichever way you go, you still need to prevent spanning tree from blocking the port, so either tune spanning tree to make sure second link is forwarding for the voice vlan or don't allow voice vlan on first trunk.
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Author Comment

by:Iamdriver38
ID: 37009315
I had created a trunk on between the two switches and tagged all the VOIP traffic on it and removed it from the other trunk. Everything from Sw B couldn't connect to the voice servers on Sw A and when I looked it was because SW A was blocking the trunk because, I assumed it was detecting a loop.

Interestingly enough SWB shows the 2nd trunk as FORWARDING but I again assumed that was because SWA was bothing and therefore from SWB's perspective there wasn't a switch loop. I am sure there is probably something I need to change with STP but I'm at a loss as to what it is. I'm not really familar with these HP switches

VLAN 82 is the VOIP

spanning-tree
spanning-tree Trk1 priority 4
spanning-tree Trk2 priority 4
spanning-tree Trk3 priority 4
spanning-tree config-name "T10"
spanning-tree config-revision 1
spanning-tree instance 1 vlan 66 72 82 86 100
spanning-tree instance 1 priority 0
spanning-tree instance 2 vlan 28 48 76 78 92 94
spanning-tree instance 2 priority 1
spanning-tree instance 3 vlan 32 38 166
spanning-tree instance 3 priority 2
spanning-tree priority 0

@donjohnston - I could just us access links for the vlan but we wanted to take advantage of the multiple links within the trunks for both available bandwidth and redudancy provided within the trunks.
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Expert Comment

by:rochey2009
ID: 37010824
did you remove the voice vlan from both ends of the trunk?
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Author Comment

by:Iamdriver38
ID: 37018313
Here's a general outline of the steps I followed.

1.) Created trk3 by adding 3 ports and verified the trunk was in an UP and SUCCESSFUL LACP state.
2.) added VLAN 82 tagging
3.) remove trk1 tagging for VLAN82 (on both switches)
4.) All devices on Switch A can connect to the voice server, devices on switch B lose connectivity to the server on SWA.
5.) I note that trk3 is blocking on switch B

I am going to call HP at this point, but if I create another STP instance and just add VLAN 82 to that instance with tagging only on trk3 will that trunk come up?

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Author Comment

by:Iamdriver38
ID: 37018428
Here's very basically want I have been asked to accomplish Desired topolgy
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Accepted Solution

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rochey2009 earned 2000 total points
ID: 37019063
Yes, try putting the voice VLAN in it's own Spanning tree instance and make sure switch B becomes the root bridge for that STP instance.
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Author Comment

by:Iamdriver38
ID: 37019133
ok thanks, I'll try that during the maintenance window tonight and see what happens.
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LVL 17

Expert Comment

by:rochey2009
ID: 37039576
did you have any luck?
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Author Comment

by:Iamdriver38
ID: 37056665
Yes thank you, I created a new STP instance for that vlan and while that did not work, changing the priority for the trk3 within that instance to priority 1 finished it off. Either way I would have had to create a new instance. Sorry for the delay.
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Author Closing Comment

by:Iamdriver38
ID: 37056668
THANK YOU. The new instance and changing the priority of the trunks fixed the problem.
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