From: Guyler, Rik (rguyler@shp-dayton.org)
Date: Wed Sep 19 2007 - 09:31:00 ART
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_note09186a00800949
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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