A quick correction -- It seems the lowest you can make max_age is actually 6 seconds : P So .... again if you wanted a 14 second convergence time you could set max_age to 6 seconds and forward-delay to 4 seconds.
max_age (6 sec) + 2x forward-delay (8 seconds) = 14 seconds On Wed, Dec 9, 2009 at 5:05 AM, Joe Astorino <[email protected]> wrote: > Hello, > > The max_age timer is how often a switch actually saves it's BPDU > information. It is part of the your overall STP convergence when there is > an INDIRECT link failure. Imagine the following simple network: > > SWA > / \ > SWB----SWC > > Assume SWA is the root bridge. Therefore, all it's ports are forwarding. > Assume SWB has the designated port on the SWB/SWC segment so it's port > facing SWC is forwarding. The SWB/SWA and SWC/SWA links are root ports. The > port facing SWB on SWC is blocking. Now imagine the SWA/SWB link goes down. > Now SWB does not get BPDUs from the root because the link failed...it also > isn't receiving any BPDUs from the path SWA --> SWC --> SWB because the link > facing SWB on SWC is in the blocking state currently. Therefore, SWB > basically thinks he is the root and starts sending inferior BPDUs towards > SWC. THIS is where max_age comes in. SWC will IGNORE these BPDUs until > max_age expires (20 seconds by default). After max_age expires, > spanning-tree will converge -- SWC will become the designated port on the > SWB-SWC segment. > > To answer your question -- When you have an INDIRECT link failure you must > wait max_age + 2x forward-delay to converge. So, if you are dealing with an > indirect link-failure and you want to tweak how fast STP takes to converge, > you can play with forward-delay , max_age or both. Lets say you wanted STP > to converge in this example in 14 seconds instead of 50 seconds. You could > make max_age = 4 seconds and forward-delay = 5 seconds so max_age + 2x > forward-delay would be 14 seconds. > > 2009/12/8 Iwan Hoogendoorn <[email protected]> > > César, >> >> 1 question at the time :-) >> Can you be more specific with your question? >> >> -- >> Regards, >> >> Iwan Hoogendoorn >> CCIE #13084 (R&S / Security / SP) >> Sr. Support Engineer – IPexpert, Inc. >> URL: http://www.IPexpert.com >> >> >> >> 2009/12/8 César Martínez Segura <[email protected]>: >> > Hi guys, >> > >> > Could anybody explain me exactly the meaning of this parameter? For my >> > readings, max-age is the time that a switch store a BPDU. Knowing that, >> > seeing a question is IPExpert asking for how a switch can detect the use >> of >> > a link in 10s, the answer is configuring in all the switches --> span >> vlan >> > 1-4094 max-age 10. Could anybody explain me why? And, apart from that, >> why I >> > don't have to take care about the forwarding delay? >> > >> > Thanks, >> > Cesar. >> > >> > _______________________________________________ >> > For more information regarding industry leading CCIE Lab training, >> please >> > visit www.ipexpert.com >> > >> > >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> > > > > -- > Regards, > > Joe Astorino CCIE #24347 (R&S) > Sr. Technical Instructor - IPexpert > Mailto: [email protected] > Telephone: +1.810.326.1444 > Live Assistance, Please visit: www.ipexpert.com/chat > eFax: +1.810.454.0130 > > IPexpert is a premier provider of Classroom and Self-Study Cisco CCNA (R&S, > Voice & Security), CCNP, CCVP, CCSP and CCIE (R&S, Voice, Security & Service > Provider) Certification Training with locations throughout the United > States, Europe and Australia. Be sure to check out our online communities at > www.ipexpert.com/communities and our public website at www.ipexpert.com > > > -- Regards, Joe Astorino CCIE #24347 (R&S) Sr. Technical Instructor - IPexpert Mailto: [email protected] Telephone: +1.810.326.1444 Live Assistance, Please visit: www.ipexpert.com/chat eFax: +1.810.454.0130 IPexpert is a premier provider of Classroom and Self-Study Cisco CCNA (R&S, Voice & Security), CCNP, CCVP, CCSP and CCIE (R&S, Voice, Security & Service Provider) Certification Training with locations throughout the United States, Europe and Australia. Be sure to check out our online communities at www.ipexpert.com/communities and our public website at www.ipexpert.com
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