The holddown timer is more or less a sanity check to the invalid timer, it guards against the router learning the same route from another update that has same or worse metric so the features complement each other. If you think about it that way, it make sense that would run at the same time as the invalid period.
Hope that helps clear things up Cheers, Donald Robb Productive Networks / Network Consultant ______________________________________________________________ CCIE Written, CCIP, CCSP, CCDP, CCNP, CCNA: Voice, JNCIP, SCP, MCSA 2003, Security+, CCSE.R65, PACE Experts-Exchange: Guru - R&S -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of CCIE KID Sent: January-22-12 12:51 AM To: Matthew P. Smith Cc: [email protected]; [email protected] Subject: Re: [OSL | CCIE_RS] Correct Understanding the RIP timers! Hi Both the Holdown and Invalid run parallely. As far as i understood the logic. In Invalid Time period, if there is any other update for the same route is updated ( The metric can be worse or same ) can be updated But in Hold Time period, If there is any other worse update or the same metric update reaches, it would discard it, So my question is how can these two timers can run parallely, How can thsi solves the purpose Because both the timers have contrasting software feature, Because the trigger is different, In Invalid the trigger is to update even the worst metric, But in Hold Time the trigger is not to update the worst metric, How this can be parallel. Is there any demarcation point for this.. I may be wrong. Can any expert correct me. On Sun, Jan 22, 2012 at 3:02 AM, Matthew P. Smith <[email protected]>wrote: > Though debugs are good, you can test this just by shutting down the > interface while watching the clock. > > When I did this, the route got pulled from the routing table 3 minutes > after the last hello(invalid timer). > > The route got pulled from the rip database after another 60 > seconds(flush timer). Keep in mind that according to Cisco, the flush > timer is 4 minutes, not 60 seconds) > > The hold down timer lasts for 3 minutes and begins after the route > goes invalid. If an advertisement for the invalid route is heard > before the hold down timer expires, it will be ignored under certain circumstances. > > BUT I'm not 100% sure if this works. Will an update identified by the > hold down timer update the flush timer? Or what if the update comes in > through a different interface or from a different router ID. Would the > advertisement still be subject to the flush and/or hold down timers? > > I guess I need to lab this out again. > But this time from different router IDs and incoming interfaces. > And before and after the flush timer expires. > Only 4 more tests to put this to bed :) > > On Jan 20, 2012, at 5:58 PM, Bob McCouch <[email protected]> wrote: > > > The output from my lab below was from 'debug ip rip database' and > > 'debug ip routing'. > > > > Bob > > -- > > Sent from my iPhone, please excuse any typos. > > > > On Jan 20, 2012, at 1:15 PM, "[email protected]" > > <[email protected]> wrote: > > > >> Hello > >> > >> What is the output of debup ip rip ? > >> -----Original Message----- > >> From: Rostam Sohrab <[email protected]> > >> Sender: [email protected] > >> Date: Fri, 20 Jan 2012 09:31:35 > >> To: Bob McCouch<[email protected]> > >> Cc: [email protected]<[email protected]> > >> Subject: Re: [OSL | CCIE_RS] Correct Understanding the RIP timers! > >> > >> Thanks to Bob & Donald! > >> > >> Those were certainly superb explanations making the understanding > pretty clear for me! > >> > >> -RS > >> > >> > >> ________________________________ > >> From: Bob McCouch <[email protected]> > >> To: Rostam Sohrab <[email protected]> > >> Cc: "[email protected]" <[email protected]> > >> Sent: Friday, 20 January 2012 8:51 AM > >> Subject: Re: [OSL | CCIE_RS] Correct Understanding the RIP timers! > >> > >> > >> Best way to see this is to lab it up. I set up a very simple > >> network > with R1 and R2 connected via ethernet. I advertised a loopback from R2 > into RIP, and then on R2 set the ethernet interface passive to stop > routing updates without giving IOS any hints by dropping the > interface. Here's what > happened: > >> > >> R1#sh ip ro | b Gate > >> Gateway of last resort is not set > >> > >> 10.0.0.0/24 is subnetted, 2 subnets > >> R 10.1.0.0 [120/1] via 10.1.124.2, 00:00:12, FastEthernet0/0 > >> C 10.1.124.0 is directly connected, FastEthernet0/0 > >> > >> R1#sh clock > >> 22:03:17.475 UTC Wed Jan 19 2011 > >> R1#!This is when I set Fa0/0 passive on R2 > >> > >> R1# > >> Jan 19 22:05:56.975: RIP-DB: invalidated route of 10.1.0.0/24 via > 10.1.124.2 > >> Jan 19 22:05:56.979: RT: delete route to 10.1.0.0 via 10.1.124.2, > >> rip > metric [120/1] > >> Jan 19 22:05:56.979: RT: no routes to 10.1.0.0, entering holddown > >> Jan 19 22:05:56.987: RIP-DB: Remove 10.1.0.0/24, (metric > >> 4294967295) > via 10.1.124.2, FastEthernet0/0 > >> > >> R1#sh ip ro | b Gate > >> Gateway of last resort is not set > >> > >> 10.0.0.0/24 is subnetted, 2 subnets > >> R 10.1.0.0/24 is possibly down, > >> routing via 10.1.124.2, FastEthernet0/0 > >> C 10.1.124.0 is directly connected, FastEthernet0/0 > >> > >> R1# > >> Jan 19 22:06:56.991: RIP-DB: garbage collect 10.1.0.0/24 Jan 19 > >> 22:06:56.995: RT: delete subnet route to 10.1.0.0/24 > >> > >> R1#sh ip ro | b Gate > >> Gateway of last resort is not set > >> > >> 10.0.0.0/24 is subnetted, 1 subnets > >> C 10.1.124.0 is directly connected, FastEthernet0/0 > >> > >> > >> So 3 minutes after the last received update, the route was marked > invalid, and 60 seconds after that the route was flushed. So all > timers are running concurrently, the update timer, the > invalid/holddown timers, and the flush timer. > >> > >> > >> Bob > >> > >> > >> On Thu, Jan 19, 2012 at 6:56 AM, Rostam Sohrab > >> <[email protected]> > wrote: > >> > >> > >>> > >>> I have a little confusion in the understanding of RIP timers. > >>> > >>> First the basics... > >>> > >>> update timer is 30 secs --> Invalid timers should be 3 times of > >>> update > i.e 90secs but the default is 180secs --> Holddown timers should be 3 > times of update i.e, 90secs but the default is 180secs --> Flush > timer, default is 240 secs. > >>> > >>> Now there are three parts to my question... > >>> > >>> The first question might sound silly but for the sake of a clear > understanding I'll write it. > >>> > >>> > >>> 1. Does the RIP updates timers work is series? i.e after one > >>> elapses > the other starts? > >>> > >>> ex: once U-30sec is over --> Invalid starts and runs for 180 secs > >>> --> > Holddown starts and runs for another 180secs --> And finally flush > timer starts and runs for 240secs. > >>> > >>> Here the total time would be 30+180+180+240=630secs until a route > >>> is > flushed out which is looking quite unreasonable! > >>> > >>> 2. Does the Invalid, Holddown & flush timers work is parallel? > >>> > >>> ex: once U-30sec is over -> Invalid, Holddown runs for 180secs > >>> along > with the flushtimer which runs for 240secs? > >>> > >>> Here the total time would be 30+240=270secs until a route is > >>> flushed > out which looks very much acceptable. > >>> > >>> > >>> 3. And why does the Invalid & Holddown timers run in parallel, if > >>> all > they do? > >>> > >>> Because at the end of these two timers (IT & HDT) it would take > another 60secs for flush timer to flush out the route, which means > that all the timers IT/HDT/FT are kicking off at the same time > immediately after update timer expires! > >>> > >>> I think I'm just complicating what is supposed to be a simple > understanding!!! > >>> > >>> -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 > _______________________________________________ > 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 > -- With Warmest Regards, CCIE KID CCIE#29992 (Security) _______________________________________________ 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
