Hi Cesar, You are exactly correct. Max-age will only be in the equation for indirect failures. If you plug a pc in, it will come up in 2x the forward-delay. There is no need for it to wait max-age.
You have the theory now, but never assume anything. When in doubt ask the proctor and be very careful of exactly what they are asking of you. Try a debug spanning-tree sometime while you play with things and you can see exact times Regards, Joe Astorino - CCIE #24347 R&S Technical Instructor - IPexpert, Inc. Cell: +1.586.212.6107 Fax: +1.810.454.0130 Mailto: [email protected] -----Original Message----- From: César Martínez Segura <[email protected]> Date: Wed, 9 Dec 2009 13:39:55 To: Joe Astorino<[email protected]> Cc: Iwan Hoogendoorn<[email protected]>; <[email protected]> Subject: Re: [OSL | CCIE_RS] max-age Hello Joe, Really good explanation. It applies for ports connected between switches but what about a port that is connected to a PC? I mean, if a port connected to a PC in SWB goes up, another port in SWC connected to another PC wants to transmit traffic to it, we have to wait just only 2xfw delay (30 sec by default) without taking care about the max-age, is correct? Max-age only affect to indirect fails between swithches, isn't it? Continuing with that, if a question says that a port (without specifying which port) has to do forwarding of traffic in 44s, I have to assume that they are speaking about a port that is in blocking state (a switch's port connected to a switch's port), so then I have to take care about 2xfw delay + max-age, and NOT a port that is connected to a PC (that only affect 2xfw delay, if I'm not wrong). It is like that? Thanks, Cesar. 2009/12/9 Joe Astorino <[email protected]> > 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 > > >
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