Question

When to use spanning-tree portfast trunk

Asked by: dsanc

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?
Thanks

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Asked On
2009-05-18 at 21:47:26ID24419828
Tags

Cisco

Topics

Network Switches & Hubs

,

Network Operations

,

Networking Protocols

Participating Experts
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Answers

 

by: that1guy15Posted on 2009-05-18 at 22:05:47ID: 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.

http://www.techexams.net/forums/ccnp/38674-spanning-tree-porfast-trunk.html
http://www.groupstudy.com/archives/ccielab/200408/msg00579.html

 

by: equarandoPosted on 2009-05-19 at 00:11:31ID: 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"

 

by: lanboyoPosted on 2009-05-19 at 03:39:41ID: 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.

 

by: that1guy15Posted on 2009-05-19 at 08:07:33ID: 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.

 

by: lanboyoPosted on 2009-05-19 at 09:24:11ID: 24423766

Yes, or a router switch tagged connection. If you have any issues with.using the command portfast bpduguard disable, don't use portfast.

20120131-EE-VQP-002

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