stp convergence time =50s or 30-50s? why?

TIA,
st

aaabbb16@hotmail.com wrote:
For regular STP with default timers on Cisco equipment and properly
configured ports - it is 30 seconds.

Regards,
Andrey.

On 26 Jun, 05:26, Andrey Tarasov <and...@email.com> wrote:
Hmmm. I would disagree with that.

I too was somewhat confused by observing that re-convergence
can take either about 30 seconds or about 45 seconds (maybe 35 and
50?).

I believe that it is like this.

For a port that is not connected that gets connected STP has to go
through
all of the states

Blocking
Listening
Learning
Forwarding
45-50 seconds - If I recall correctly

For a port that is already in the network and is Blocking
The transition to Forwarding is about 30-35 seconds

The default timers will be easy to find on the web.

Note that the times do not really range over the interval indicated
but I have specified a range since I cannot remember the correct
times and BPDUs are sent only every two seconds so there will
be a range of times introduced by the port state change possibly
occurring just before or just after a BPDU tx or rx event.

Of course there are other considerations.

For a newly connected port then there may be
physical speed/duplex negotiation
etherchannel negotiation
trunking negotiation

There are also various STP optimisations
portfast
uplink fast
backbone fast

Lastly of course there is Rapid STP which is substantially changed
from
traditional STP and has much lower convergence times. I have not
worked
with it but have the idea that convergence times of one to a few
seconds are
reasonable.

On 6ÔÂ26ÈÕ, ÉÏÎç6ʱ24·Ö, Bo...@hotmail.co.uk wrote:
Thanks,
I think 50s=2x15s(forwarding delay)+20s(max age time)
so the max. convergence time is 50s and min. is 30s. right?
why does max age time is from 0-20s?

st

Bod43@hotmail.co.uk wrote:
That's fine. How about some facts?

Why? 2 x forwarding delay is 28.5 sec. Where are additional 15-20 sec
coming from?

So what's the difference between newly connected vs already connected?

Not relevant to original question. While etherchannel/trunking
negotiation indeed adds time, it's not part of STP convergence.

That's enabled on edge ports only and doesn't affect convergence time at
all.

Cisco extensions and not part of original 802.1D spec.

Again, Rapid STP is completely different beast.

Regards,
Andrey.

Andrey Tarasov wrote:
Andrey,

to sum it up. Going through all stp states takes 30 seconds! Neither less nor
more

Andre

<aaabbb16@hotmail.com> wrote in message
news:e0eb64c3-9850-421f-b070-b51f9f2d31ce@r37g2000prm.googlegroups.com...

Let's say the lowest cost root path includes 3 switches between you and the
root,
and there is also an inferior path to the root with higher cost.

If something should affect the continuity between , say, the root and the
first switch closest to the
root on your "preferred" path, your switch will not detect the failure until
20 seconds pass
without seeing any of the 'preferred' bpdus. After realizing there is a
failure (20 seconds),
your switch will then go through the normal 15 listening/15 learning second
convergence.
But that doesn't happen until your switch realizes there is a problem, which
too 20 seconds
of no-show bpdus up front. Total time - 50 seconds.

John Agosta wrote:
My bad. Indirect failure will indeed produce 50 seconds convergence.
Convergence for direct failure is 30 sec though.

Regards,
Andrey.