PVST+ on Local Switch

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Feb 11th, 2008
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If a 6500 series switch (with PVST+ enabled) were to lose connectivity on a root port, and STP had to reconverge, would local communication within a vlan on the same switch be affected?

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lamav Mon, 02/11/2008 - 13:33
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As STP reconverges, traffic for the specific VLAN that has caused the reconvergence will be effected.

This is why you should design a deterministic network that has the root switch and the secondary for each VLAN already configured. In other words, "rig" the election to avoid an interruption in data flow.


sometechguy Mon, 02/11/2008 - 16:57
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Thank you for your response. I understand the need for such a design. I am trying to determine if data traffic within the same vlan on the same switch will be affected.

For example, if I have two servers in the same Vlan5 on the same switch, connected to ports gi7/1 and gi7/2, will the IP conversations between these two servers be interrupted if the fiber link to the "root" switch is disturbed OR is local traffic on the switch safe while STP reconverges. The traffic I am interested in will not leave the switch.

gauravshar@hcl.in Tue, 02/12/2008 - 00:11
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As you said that you are having PVST+ enabled and using it in your LAN/VLAN environment, you must have configured 'portfast' on access ports of servers. That portfast feature actually prevents some application-timeouts at the time of STP convergance.

No doubt your data communication between the servers will be hampered momentarily due to STP convergance but portfast will take care of your servers' ease to get the port back up/forwarding very early.


lamav Tue, 02/12/2008 - 17:23
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If you have portfast enabled on those server ports, they will not participate in the root bridge election nor will they go through any of the STP port states.

So, my answer is no, communications should not be effected.


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