That's a very valid question and one that I get asked often :-) Generally speaking, you are right - as soon as PortFast receives a BPDU it will be disabled and the port transitioned into the appropriate state (remain forwarding or end up being blocked/discarding).
However… There is that brief period of time before a BPDU has been received during which, depending on the amount of the traffic in your network, bad things could happen due to the loop that was briefly formed. I personally think that warning message is misplaced. It should appear when you configure BPDU Filter on the interface and not PortFast, but that's just me :-) -- Marko Milivojevic - CCIE #18427 (SP R&S) Senior CCIE Instructor / Managing Partner - IPexpert On Thu, Apr 4, 2013 at 2:39 AM, Quentin Huberty <[email protected]>wrote: > Hi all,**** > > ** ** > > Is anybody know why the message below appears when portfast is activated ? > **** > > ** ** > > %Warning: this command enables portfast by default on all interfaces. You* > *** > > should now disable portfast explicitly on switched ports leading to hubs, > **** > > switches and bridges as they may create temporary bridging loops.**** > > ** ** > > I mean, I tested and each time I received BPDU on interface where portfast > is enabled (per interface or globally) the portfast is automatically > disabled and STP run...**** > > ** ** > > How a loop can be created ? > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
