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CyberOptic
Asked: 2011-09-15 04:18:04 +0800 CST

Stackwise and RSTP states of other uplinks

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Assuming I've got four C3750X, each side stacked with Stackwise Plus and using RSTP:

C1 -----10Gbit----- C2
|                    |
|                    |
SW                  SW
|                    |
|                    |
C3 -----10Gbit----- C4

Would the second 10Gbit-uplink in RSTP alternate or backup state?

Edit: The two 10Gbit lines are provided by two different carriers with two different round-time-trips (due to different fibre lengths)

cisco spanning-tree

3 Answers

  1. One of the 10Gig links would be in alternate blocking state and one would be forwarding if I read that diagram correctly.

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  2. Best Answer

    It depends on how you configure STP.

    PVSTP and PVSTP+ supports per-VLAN STP, wich means that you can chose one uplink for a certain set of VLAN's and another uplink for other VLAN's.

    Either way - there is no need to run separate uplinks when you have a switch stack on each end. Just configure a etherchannel between the switches, using one port on each physical switch. This will give you the redundancy (and load balancing) you are after.

    For more information: http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_53_se/configuration/guide/swethchl.html#wp1342634

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  3. In that topology, the blocked port will be in Alternate state.

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