When to use spanning-tree portfast trunk

Posted on 2009-05-18
Last Modified: 2012-08-14
I have 2 switches with 2 redundancy conections,  in all the ports, it is configures the command spanning-tree portfast trunk.

I am getting a lot of topology changes from this port, I know portfast should be use to access port, I want to figure out why, they configure it with the portfast trunk.

Does anyone have idea of what this command do?
Question by:dsanc
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LVL 23

Assisted Solution

that1guy15 earned 75 total points
ID: 24418564
I myself have never ran into a situation that would need STP port-fast on a trunk link. But here are a few post with your same question.

Assisted Solution

equarando earned 25 total points
ID: 24419227
Yes, you are right about spanning-tree portfast should be only used on access ports. But I guess for some odd reason if you want to turn portfast on your trunk links cisco lets you with that command.

Taken from cisco's command database...

"Router(config-if)# spanning-tree portfast trunk
%Warning:portfast should only be enabled on ports connected to a single
 host. Connecting hubs, concentrators, switches, bridges, etc... to this
 interface  when portfast is enabled, can cause temporary bridging loops.
 Use with CAUTION"
LVL 10

Accepted Solution

lanboyo earned 150 total points
ID: 24420330
Portfast trunk is for when you are quite positive that there will be no loops or redundant routes on this link. A trunk to a dot1q aware host, a dot1q aware point to point, etc. Never to a network that needs a redundant l2 path. Look at fast failove r or rapid spantree if the ordinary time periods are excessive for your needs.
LVL 23

Assisted Solution

that1guy15 earned 75 total points
ID: 24422839
One reason I am seeing for it is when you connect an ip phone up to a port and need to set it to trunk due to multiple clans (voice and data). But from what I'm reading setting a voice vlan on the interface is the recommended solution.

A use for it was suggested in one of the links I provided, which was when connecting a virtualization server (hosting
multiple vlans to a switch.
LVL 10

Assisted Solution

lanboyo earned 150 total points
ID: 24423766
Yes, or a router switch tagged connection. If you have any issues with.using the command portfast bpduguard disable, don't use portfast.

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