From: Charles McGeoch \(Europe\) (charles.mcgeoch@uk.didata.com)
Date: Wed Sep 19 2007 - 13:27:53 ART
Hi Scott,
I had a go at setting this up in my lab today. With a forwarding-delay
of 6 seconds configured on the VLAN, the amount of time it took for one
of my routers to be able to ping another router in that same VLAN was 12
seconds. This time measurement was taken from the point that the
interface became active on the router after I'd no shut the switchport
that the other router was connected too.
I'm unsure about where 32 seconds comes into things (presumably the
default max-age time of 20sec). Would this be relevant if the link has
been between two switches and in a blocking state in the first place due
to spanning-tree?
Regards
Chaz
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Scott Morris
Sent: 19 September 2007 15:21
To: 'Gregory Gombas'; 'Guyler, Rik'
Cc: 'alexey'; 'davidytk'; ccielab@groupstudy.com
Subject: RE: STP and Routing questions
Convergence time does not include the blocking timer (20 sec) so it's
just 2
x forward-time. (listen + learn)
Therefore, set your spanning-tree forward-time to 6 and you'll get 12
second
convergence and 32 second initial delay when first connecting to the
switch.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
JNCIE-M
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical Training - IPexpert, Inc.
IPexpert Sr. Technical Instructor
A Cisco Learning Partner - We Accept Learning Credits!
smorris@ipexpert.com
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Gregory Gombas
Sent: Wednesday, September 19, 2007 9:40 AM
To: Guyler, Rik
Cc: alexey; davidytk; ccielab@groupstudy.com
Subject: Re: STP and Routing questions
Hi Rik,
Can you share the configuration commands needed to achieve a 12 second
convergence time?
Thanks
On 9/19/07, Guyler, Rik <rguyler@shp-dayton.org> wrote:
> Well, 50s is the default *maximum* time it will take to transition
> into the forwarding state, not the time it will take.
>
> Taken from your link:
>
> max_age
> = End-to-end_BPDU_propa_delay + Message_age_overestimate = 14 + 6 = 20
> sec
>
> 2 x forward_delay
> = end-to-end_BPDU_propagation_delay + Message_age_overestimate +
> Maximum_frame_lifetime + Maximum_transmission_halt_delay = 14 + 6 +
> 7.5 + 1 = 28.5
>
> forward_delay
> = 28.5 /2
> = 15 (rounded)
>
>
> So the maximum time it would take to transition into the forwarding
> state by default is:
>
> max_age + 2 x forward_delay = 50sec (rounded)
>
> To answer Gary's question, if all you adjusted was max_age and
> forward_delay then you're right, 14 seconds would be the minimum you
> could achieve. To get below that number you will have to adjust
> either the the hello interval or diameter. Here's the formula:
>
> End-to-end_BPDU_propa_delay
> = ((lost_msg + 1) x hello) + ((BPDU_Delay x (dia - 1)) = ((3 + 1) x
> hello) + ((1 x (dia - 1)) = 4 x hello + dia - 1 = 4 x 2 + 6 = 14 sec
>
> Message_age_overestimate
> = (dia - 1) x overestimate_per_bridge
> = dia - 1
> = 6
>
> Maximum_frame_lifetime
> = dia x transit_delay + med_access_delay = dia + 0.5 = 7.5 = 8
> (rounded)
>
> Maximum_transmission_halt_delay
> = 1
>
> Rik
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of alexey
> Sent: Wednesday, September 19, 2007 7:56 AM
> To: davidytk
> Cc: ccielab@groupstudy.com
> Subject: Re: STP and Routing questions
>
> 2007/9/19, davidytk <davidytk@netvigator.com>:
> >
> > Default the STP port from blocking to fowarding is 50s.
>
>
> Don't agree!
> http://cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00
> 800949
> 54.shtml
>
> "...The movement of a port into the listening state indicates that
> there is a change in the active STP topology and that a port will go
> from blocking to forwarding."
>
> For a definition of these changes is Max Age. But two timer Forward
> Delay responsible for the transition from BLK to FWD!
>
>
> This timer is
> > related to forward delay and max age
> >
> > 50s = 2*forward delay + max age.
> >
> > Default forward delay = 15s
> > Default max age = 20s
> >
> > I think the question is related to this item. But there is some
> > other ways to minimum the timer.
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > Of alexey
> > Sent: Wednesday, September 19, 2007 5:53 PM
> > To: ccielab@groupstudy.com
> > Subject: Fwd: STP and Routing questions
> >
> > > 1. What about max age time? The minimum max age is 6 seconds.
> > > Minimum forward delay is 4 seconds.
> > >
> > > So 6+(4*2) = 14 seconds is the minimum, isn't it?
> > >
> > > Someone please verify these numbers...
> >
> >
> > This is not true. Because the question specifically about port
> > startup (BLK
> > -> FWD), rather than on the time of convergence network (Max Age +
> > -> Forward
> > Delay + Forward Delay).
> >
> >
> > > On 9/17/07, hadek.el-ayachi@nsn.com <hadek.el-ayachi@nsn.com>
wrote:
> > > > Hi Experts,
> > > > I have the following questions:
> > > > 1- In a non root switch, make the startup time of ports in vlan
> > > > 15 equal to 12 seconds?
> >
> >
> > All changes timers should be done only at the root switch. Changes
> > timers at non-root switches will not lead to any results. Am I
right?
> >
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