rapid-pvst mode AND spanning-tree portfast trunk

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Sep 14th, 2009
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Ok, if my switches are configured for RSTP, do I still have to add "spanning-tree portfast trunk" under the dot1q interfaces??

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Jon Marshall Mon, 09/14/2009 - 08:11
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Regardless of which STP version you are using you should only use "spanning-tree portfast trunk" on ports connected to end devices such as servers that run 802.1q on their NIC's.

You should never use this command on a trunk link between 2 switches.

Having said that yes you would still benefit from this command even with RSTP.


yagnesh_tel Mon, 09/14/2009 - 08:17
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Yes, there is certain advantage of using portfast while still having Rapid convergence using RSTP.

If port does not have Portfast enabled, eventhough it will go into forwarding state quickly as per RSTP standard, it will reach that state after going through BLK,LRN. Whereas configuring portfast feature compel it to skip these states and be in forwarding state right away.

I hope that you aware of this guideline by Cisco: "You can use PortFast to connect a single end station or a switch port to a switch port. If you enable PortFast on a port that is connected to another Layer 2 device, such as a switch, you might create network loops."


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