My understanding is that timers are not involved is this scenario. See info below from Cisco's website:
"Rapid transition is the most important feature introduced by 802.1w. The legacy STA passively waited for the network to converge before it turned a port into the forwarding state. The achievement of faster convergence was a matter of tuning the conservative default parameters (forward delay and max_age timers) and often put the stability of the network at stake. The new rapid STP is able to actively confirm that a port can safely transition to the forwarding state without having to rely on any timer configuration. There is now a real feedback mechanism that takes place between RSTP-compliant bridges. In order to achieve fast convergence on a port, the protocol relies upon two new variables: edge ports and link type." http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml On Mar 10, 2011, at 9:10 AM, marc abel wrote: > Just to add a little more to this, even after tuning all the rstp > timers down to their minimum I don't see any noticeable change. I > still drop 1 packet between convergence. So I guess it's better to > keep the default timers to keep cpu usage down if it doesn't really > gain me anything to go lower. Anyone have an opinion on this? > > > On Wed, Mar 9, 2011 at 8:53 PM, marc abel <[email protected]> wrote: >> I'm steadily improving the network from little/no redundancy to >> complete redundancy. I have to pick my budget battles right now and >> frankly there are a few other places I'd rather improve first. >> Fortunately all my server switches are linked via ether-channel. >> Although no matter how many links in your bundle, if you lose your STP >> root, then you are going to have a re-convergence. I had a core switch >> roll over on me due to a "parity error" (according to TAC) a few >> months ago. Things recovered really well, but I haven't implemented >> the voice yet so I didn't have anything quite that latency dependent >> at the time. >> >> On Wed, Mar 9, 2011 at 8:38 PM, Jay Taylor <[email protected]> wrote: >>> Any chance of just doubling your links for each path? That would only >>> require 2 extra pairs of fiber to each IDF rather than uplinking each >>> switch. But then again, that 1 ping missed with RSTP was with default timers >>> and I'm sure you could trim that down. >>> >>> >>> On Wed, Mar 9, 2011 at 9:32 PM, Michael Smith <[email protected]> wrote: >>>> >>>> Well you guys are right. I've always dealt with switches that have been >>>> etherchannelled to another switch so I never really dealt with switches >>>> that >>>> are single linked like that. I just don't know the reason why anybody >>>> wouldn't etherchannel their switches together. Hey I guess you live and you >>>> learn! >>>> >>>> >>>> >>>>> Date: Wed, 9 Mar 2011 20:28:21 -0600 >>>>> Subject: Re: [OSL | CCIE_RS] Rapid Spanning Tree convergence times >>>>> From: [email protected] >>>>> To: [email protected] >>>>> CC: [email protected]; [email protected] >>>>> >>>>> Right because in my situation one of the links to the cores is going >>>>> to be in blocking state. I don't see any way around that. >>>>> >>>>> On Wed, Mar 9, 2011 at 8:25 PM, Jay Taylor <[email protected]> wrote: >>>>>> Even with HSRP and sub-second hellos you could lose pings depending on >>>>>> how >>>>>> STP needed to converge. >>>>>> >>>>>> On Wed, Mar 9, 2011 at 9:24 PM, Michael Smith <[email protected]> >>>>>> wrote: >>>>>>> >>>>>>> Well I'm talking as far as the VOIP phones go. They obviously need a >>>>>>> gateway and to not miss any pings you can always turn on HSRP. >>>>>>> I'm not saying HSRP has anything to do with spanning tree. Just >>>>>>> thinking >>>>>>> about the fact of not losing any pings. >>>>>>> >>>>>>> >>>>>>> >>>>>>> ________________________________ >>>>>>> Date: Wed, 9 Mar 2011 21:05:04 -0500 >>>>>>> Subject: Re: [OSL | CCIE_RS] Rapid Spanning Tree convergence times >>>>>>> From: [email protected] >>>>>>> To: [email protected] >>>>>>> CC: [email protected]; [email protected] >>>>>>> >>>>>>> Maybe I'm missing something but how can HSRP (or first hop redundancy >>>>>>> protocol) replace STP/Etherchannel? Even if 2 of the Catalyst >>>>>>> switches in >>>>>>> that topology were L3 gateways and ran HSRP you still need to deal >>>>>>> with the >>>>>>> L2 loop that exists. >>>>>>> >>>>>>> >>>>>>> On Wed, Mar 9, 2011 at 8:50 PM, [email protected] >>>>>>> <[email protected]> >>>>>>> wrote: >>>>>>> >>>>>>> Well if yor timers are that bad for VOIP you can always use hsrp if >>>>>>> you >>>>>>> don't want to use the etherchannel option. You can tune hsrp down to >>>>>>> milliseconds if you wanted to. Of course your distribution switches >>>>>>> need to >>>>>>> support an enhanced IOS image >>>>>>> >>>>>>> Sent from my Verizon Wireless Phone >>>>>>> >>>>>>> ----- Reply message ----- >>>>>>> From: "Jay Taylor" <[email protected]> >>>>>>> Date: Wed, Mar 9, 2011 7:57 pm >>>>>>> Subject: [OSL | CCIE_RS] Rapid Spanning Tree convergence times >>>>>>> To: "marc abel" <[email protected]> >>>>>>> Cc: <[email protected]> >>>>>>> >>>>>>> >>>>>>> Enable portfast on the host ports and you'll see a much quicker >>>>>>> transition. >>>>>>> Just labbed this up and with portfast enabled I lost a single ping >>>>>>> during >>>>>>> the failover. Without it enabled I lost 12. >>>>>>> >>>>>>> For the VoIP question - in production I'd recommend building with >>>>>>> Etherchannels just so STP never needs to converge. >>>>>>> >>>>>>> >>>>>>> On Wed, Mar 9, 2011 at 5:41 PM, marc abel <[email protected]> wrote: >>>>>>> >>>>>>>> I have 4 switches connected in a loop. >>>>>>>> >>>>>>>> Cat1-------------Cat2 >>>>>>>> | | >>>>>>>> | | >>>>>>>> Cat3----------Cat4 >>>>>>>> >>>>>>>> >>>>>>>> Cat 1 is the root, Cat 2 is the secondary root. All the switches >>>>>>>> are >>>>>>>> set to RPVSTP and I have confirmed that show spanning-tree shows >>>>>>>> RSTP >>>>>>>> as the protocol. Cat 4 shows it's interface to cat3 as it's root >>>>>>>> port >>>>>>>> and the interface to Cat3 as the Alternate. I have not tuned any >>>>>>>> timers. >>>>>>>> >>>>>>>> What should be the convergence time in this situation? >>>>>>>> >>>>>>>> If I run a ping from a host attached to Cat4 to a host attached to >>>>>>>> Cat1 and then I shut the Cat1-Cat3 interface (on the Cat1 side) it >>>>>>>> takes about 32 seconds before pings pick back up. I thought RSTP >>>>>>>> was >>>>>>>> supposed to converge in about 6 seconds? >>>>>>>> >>>>>>>> Another question, what is the fastest recovery time we can tune >>>>>>>> down >>>>>>>> to from RSTP? How do others tune this for VOIP? I know that I can >>>>>>>> get >>>>>>>> sub second convergence from OSPF but not all my switches have an >>>>>>>> appropriate image to run ospf. >>>>>>>> >>>>>>>> >>>>>>>> Thanks in advance. >>>>>>>> >>>>>>>> Marc >>>>>>>> _______________________________________________ >>>>>>>> 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 >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>> >>>>>> >>> >>> >> > _______________________________________________ > 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
