MST with Stacking

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Jul 22nd, 2008
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has anyone used cat 3750 stacking with Multiple spanning tree (802.1s) active to group vlans on the stacking switches?

in the attachment, i have two 3750 in the stack. the top switch is the master with Vlan 4 active on all ports and trunking to core 1. the seconda switch is the slave, also trunked to core 2 and vlan 5 active on all ports. the idea is to have just 2 MST instance active within the stack ring.

If trunk on the slave to core 2 fails, all traffic for vlan 5 should go through the trunk to core 1 through the master switch.

is this a good design?

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francisco_1 Wed, 07/23/2008 - 03:30
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have i confused anyone?

Please, please respond. even if you just say hi i dont mind. :)


Giuseppe Larosa Wed, 07/23/2008 - 08:59
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the stack member switches are interconnected via the stackwise cables but from the STP point of view these are just trunk ports carrying all the vlans defined on the stack and the BPDU frames.

So then it comes to elect a root port the whole stack behaves as a single switch.

See the following link

These statements are true when the switch stack is operating in PVST+ or rapid-PVST+ mode:

•A switch stack appears as a single spanning-tree node to the rest of the network, and all stack members use the same bridge ID for a given spanning tree. The bridge ID is derived from the MAC address of the stack master.

Try to look what happens with MST starting from that link above

hope to help



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