A port configured with BPDU filtering will not send or receive BPDU frames with another device. If there's a loop in the layer 2 topology involving a port configured with BPDU filtering you'll see error messages in the log about MAC addresses flipping from one port to another over and over again. Enabling BPDU filter essentially disables spanning tree on that port.
As far as root elections go, it doesn't directly influence that. It can prevent a switch from participating in the election process altogether if BPDU filtering is segmenting the spanning tree topology. On Fri, Apr 5, 2013 at 11:50 AM, <[email protected]> wrote: > Do you mean if it is not configured under the right interfaces ? In this > case it can cause root bridge election problems and ports going for > learning to blocking several times > > > -----Original Message----- > From: Marko Milivojevic <[email protected]> > Sender: [email protected] > Date: Thu, 4 Apr 2013 13:33:18 > To: Tony Singh<[email protected]> > Cc: OSL Routing and Switching<[email protected]> > Subject: Re: [OSL | CCIE_RS] Portfast LOOP > > BPDUs are not *added* to the frames. They are separate control frames sent > by the switches. BPDU Filter does not create temporary loops, if used > improperly it creates permanent loops that can bring down the whole > network. > > -- > Marko Milivojevic - CCIE #18427 (SP R&S) > Senior CCIE Instructor / Managing Partner - IPexpert > > > On Thu, Apr 4, 2013 at 12:51 PM, Tony Singh <[email protected]> wrote: > > > > > Hi Marko > > > > Can you expand if possible on why bpdu filter would cause temp loops? Are > > you saying that the bpdu is stripped from an Ethernet frame when this > > happens? > > > > This may be a stupid question but when we filter bpdu's then I presume > > this doesn't include the whole 802.3 frame, as I understand it a bpdu is > > added to the payload of the 802.3 Ethernet frame and is 35 bytes in size > or > > am I going completely off the scales here and have I got knowledge > gaps... > > > > Or are we talking STP BPDU's for control only... > > > > To picture my understanding: > > > > > > > http://www.google.co.uk/search?q=bpdu+where+in+ethernet+frame&oe=UTF-8&hl=en&client=safari&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=RNRdUaedD4iL4AT6roCwAw&biw=768&bih=928&sei=SNRdUeKnIei00QW54YHoAQ#biv=i%7C4%3Bd%7CgoRoh1hn961EyM%3A > > > > -- > > BR > > > > Tony > > > > Sent from my iPad > > > > On 4 Apr 2013, at 19:49, Marko Milivojevic <[email protected]> wrote: > > > > > 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 > > > _______________________________________________ > 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 > _______________________________________________ > 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 > _______________________________________________ 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
