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spanning-tree portfast on a switchport to another switch

Posted on 2010-09-09
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Last Modified: 2012-05-10
We have a simple network. Locally, we have 4 2950's behind a 2611. We
have about 60 PCs. We have instances where an inexpensive 4-port DLINK switch (something
meant for a personal PC or a small office) joins 2 - 4 PCs to a single switchport on a
2950 switch. On the Cisco config of these switchports, we have entered "no spanning-tree
portfast."

We often move PCs. When we do, the location of the DLINK switches sometimes change,
requiring us to change the config on the relative Cisco switchports. My question: Is there
any real danger in having a small 4-port DLINK switch with 2 - 4 PCs plugged into a Cisco
switchport with spanning-tree portfast enabled?
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Question by:meade470
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kf4zmt earned 250 total points
ID: 33640238
No danger as long as the dlink ONLY connects to one switch port.  The danger comes in when the dlink connects to multiple switches/hubs where a loop could be created.  If you are certain the dlink only connects to one switch and to only one port on that switch you can safely enable portfast.
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by:Don Johnston
Don Johnston earned 250 total points
ID: 33642181
>Is there any real danger in having a small 4-port DLINK switch with 2 - 4 PCs plugged into a Cisco
switchport with spanning-tree portfast enabled?

No. Then again, there's not much to gain either. The big advantage to portfast is that the port can forward traffic as soon as a link is detected (instead of going through the 30 second listening/learning delay). But with a switch connected to the port, the link will always be up so portfast isn't going to make any difference.

If it were me, I'd leave portfast off on those ports.



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by:meade470
ID: 33646300
Thanks, guys. I agree with both ideas and will have to make a decision.
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