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If I have two switches connected to one another by a fibre link, and each of those switches is also connected into a local switch, and those two local switches are linked, I'm correct in thinking that irrespective of VLAN's or any L3 configuration, I'll have an L2 loop that STP/RSTP will need to sort out aren't I?

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VLAN 100 and VLAN 200 will only exist on the top two switches so the link between those two switches will be only handle tagged traffic on VLAN 100 and VLAN 200.

The switches are dedicated to iSCSI and vMotion traffic and only need physically connect to the main network to allow management of the switches and of the iSCSI SAN.

One option would be to keep them physically separate and put a basic firewall between them and the main LAN doing away with the loop.

Thanks ever so much.

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+1 - I wish everyone had details and graphics this specific! –  Mark Henderson Dec 6 '10 at 1:17
    
+1 Well written question. Technically some switches can be configured so you don't need STP; in all normal circumstances I would just enable STP and let it sort things though. –  Chris S Dec 6 '10 at 1:35
    
I agree with Mark. +1 for the diagram, and good question detail. It looks like a Gliffy diagram, which you can sign up for here: gliffy.com (free!) –  JakeRobinson Dec 6 '10 at 1:35
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1 Answer

up vote 7 down vote accepted

Yes, this would be a loop for which you would need STP.

When you have trunks which don't carry all VLANs everywhere, you want to use some care in selecting the switch to be STP root. In particular, if either of the bottom switches is the STP root, then the top switches will resolve the loop by blocking the trunk forming the top of the box -- which is the only transit for VLAN 100 and 200, which I suspect is undesirable.

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Thanks, yet I thought about the VLAN tagging/trunking question after I posted my original question - the Procurve's default to MSTP which is HP's implementation of STP where you have VLAN's, least that's my understanding. –  Hutch Dec 6 '10 at 13:15
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