Re: mac-address ageing per vlan

Ok team, lab testing done. The lab test appeared to be a good way to test
this. You will need to check the commands on both switches and verify
everything before starting the pings from one of the two routers.

I had two switches in between the routers with two links between them; SW1
and SW2 were my switches. SW2 is root. On SW1, one link was Alt, and the
other was Fwd. All is well thus far.

On SW1, I changed the port cost to a lower value on the Alt link and then
watched the changes to the mac address table and pings between R1 and R2.

Since I was making the changes on SW1, I wanted to check the affect of these
on downstream switches. (I only had one additional switch in these lab
tests ....)

Traditional spanning tree =

1) ~ 30 seconds for listening and learning transitions from Alt to Fwd. No
pings could get through during this time.
2) ~ 15 seconds for the mac address tables to be cleared from the mac
address table on SW2. I checked SW2 during this time, and the entries were
not aged out immediately, but roughly 15 seconds later.

Re-learning these mac addresses takes about the same time as spanning tree
to converge since forwarding is not yet occurring. However during the
learning phases, the switches were able to start relearning the mac
addresses.

Rapid spanning tree =

1) Less than a second to transition over from Alt to Fwd. Consistently lost
1 ping (out of about 10,000)
2) As soon as the change was made or when the alternate port was up, the mac
addresses were aged out and of course they were quickly relearned since the
ports were in forwarding mode and I had a continuous ping. I was not quick
enough in my show commands to tell if the aging process was faster that the
transition from Alt to Fwd. Rapido Amigo!

Conclusions?

1) Never run traditional spanning tree ;-)

2) It was hard for me to give an accurate number with my 'human-latency',
however for traditional STP the docs appear to be accurate for down stream
switches.

3) Never make any changes during production times ..., Duh! ;-)

Team - I will have this setup running for another day or so ... have a great
night ... time for this bear to get some sleep.

Andrew Lee Lissitz

On Sat, Nov 14, 2009 at 7:54 PM, ALL From_NJ <all.from.nj_at_gmail.com> wrote:

> Abraham, Johnny, and team,
>
> I hope all is well.
>
> Abraham - the 'accelerated aging' is the same as the default forward time
> per the docs. It is 'accelerated' from 5 minutes to 15.
>
> My theory (will try and test it later tonight after the family goes to bed)
> is that 15 seconds will be the aging time for STP, but I believe that rapid
> and mstp would age it out immediately since they would begin forwarding
> immediately. Just a theory ... unless someone else has already tested
> this.
>
> My thoughts on testing:
>
> 2 switches and two routers. The two routers will ping each other.
> Successful pings and show mac-address.
>
> On each switch I will modify the root and initial port cost. I hope to
> cause a reconfigure that will stop ping and also show the mac-address
> learned on the wrong link.
>
> We shall see ... only once I begin to test this will I see if my testing /
> theory is accurate. Have a great night team,
>
> Andrew Lee Lissitz
>
>
> On Sat, Nov 14, 2009 at 11:56 AM, Johnny B CCIE <jbccie_at_gmail.com> wrote:
>
>> This might help.
>>
>>
>>
http://books.google.com/books?id=eskSfkT3QMkC&pg=PA41&lpg=PA41&dq=accelerated
+aging+forward-time&source=bl&ots=QZgqUkVCQc&sig=tNQOBdhMfuJKJwql_DCoKlLJBgs&
hl=en&ei=jOD-Sun0AYe0tgez5Y2SDg&sa=X&oi=book_result&ct=result&resnum=1&ved=0C
AgQ6AEwAA#v=onepage&q=accelerated%20aging%20forward-time&f=false
>>
>>
>>
>> On Sat, Nov 14, 2009 at 11:50 AM, Abraham, Tharak
>> <tharakabraham_at_gmail.com> wrote:
>> > Thanks Johny !
>> > That answered my question directly but i had a confusion with
>> accelerated
>> > aging/forward delay config.and thats why this thread popped up.
>> >
>> > Andrew,
>> > Is it 15 secs that the "short aging" time the Doc refers to in the case
>> of
>> > pvst+ ?
>> > Better to test it though, i can do it tomorrow.
>> >
>> > Thanks again guys !
>> >
>> > Tharak Abraham.
>> >
>> >
>> > On Sat, Nov 14, 2009 at 6:57 PM, ALL From_NJ <all.from.nj_at_gmail.com>
>> wrote:
>> >>
>> >> I have always found this to be an interesting topic ... mainly, because
>> it
>> >> occurs automatically and we do not think much of it (except for CCIE
>> >> studies!)
>> >>
>> >> Here is the link I assume you are referring to?
>> >>
>> >>
>>
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12
.2_25_se/configuration/guide/swstp.html#wp1169222
>> >>
>> >>
>> >> Johnny mentioned the command to set the aging time manually. I think
>> he
>> >> answers your question.
>> >>
>> >> - Team - keep me honest here ...
>> >>
>> >> A couple of thoughts around this and to try and keep things clear (at
>> >> least
>> >> in my head).
>> >>
>> >> W/ rapid spt the mac address is immediately deleted when a TCN is
>> learned,
>> >> no need to rely on the aging timers per mac address. MSTP is built on
>> >> rapid
>> >> stp, so it also performs the same.
>> >>
>> >> When spt needs to converge different paths may exist throughout. What
>> >> would
>> >> happen if all the mac addresses are learned over an interface that is
>> no
>> >> longer the forwarding one? Some confusion within the switch perhaps;
>> >> especially when it starts to learn mac addresses over different
>> >> interfaces.
>> >>
>> >>
>> >> So the switch should age these mac addresses per the forwarding time,
>> and
>> >> as
>> >> the documentation mentions. This makes sense for STP.
>> >>
>> >> Does the forwarding time have affect with rapid and or mstp for
>> alternate
>> >> links? Humm ... not really. What does this mean for the aging times?
>> My
>> >> understanding is that these are aged out immediately for the vlans that
>> >> were
>> >> affected.
>> >>
>> >> Anyone see this in the docs or a lab test? I would lab test it but I
>> have
>> >> no time today till maybe late tonight.
>> >>
>> >> Can you believe I am still working on leaves and honey-do lists? Ok,
>> >> honey-do lists of course ... these never end, but still raking leaves?
>> >> Sadly true ...
>> >>
>> >> I feel like Fred Sanford from 'Sanford and son' crying about my back
>> and
>> >> heart ... no one seems to care. ;-) ... crickets and tumbleweeds are
>> all
>> >> I
>> >> hear and see when I say these things ... oh humm ... it is hard to be
>> me.
>> >> lol
>> >>
>> >> Andrew Lee Lissitz
>> >>
>> >>
>> >>
>> >>
>> >> On Sat, Nov 14, 2009 at 1:11 AM, Johnny B CCIE <jbccie_at_gmail.com>
>> wrote:
>> >>
>> >> > conf t
>> >> > mac address-table aging-time x vlan xx
>> >> >
>> >> > The default value x is 300 seconds = 5minutes.
>> >> > If you use x = 0, then you have disabled aging for the vlan in
>> question.
>> >> >
>> >> >
>> >> >
>> >> > On Sat, Nov 14, 2009 at 12:42 AM, Abraham, Tharak
>> >> > <tharakabraham_at_gmail.com> wrote:
>> >> > > Gents,
>> >> > >
>> >> > > Could you explain how to enable mac-add ageing for a particular
>> vlan ?
>> >> > >
>> >> > > Just read that accelerated-ageing for a particular vlan can be
>> linked
>> >> > with
>> >> > > STP for that vlan with the forward time.
>> >> > > i.e spanning-tree vlan x forward-time y
>> >> > >
>> >> > > Could someone add more thoughts on this ?
>> >> > >
>> >> > > Tharak
>> >> > >
>> >> > >
>> >> > > Blogs and organic groups at http://www.ccie.net
>> >> > >
>> >> > >
>> >> > >
>> _______________________________________________________________________
>> >> > > Subscription information may be found at:
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>> >> >
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>> >> >
>> >> >
>> _______________________________________________________________________
>> >> > Subscription information may be found at:
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>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >>
>> >>
>> >> --
>> >> Andrew Lee Lissitz
>> >> all.from.nj_at_gmail.com
>> >>
>> >>
>> >> Blogs and organic groups at http://www.ccie.net
>> >>
>> >> _______________________________________________________________________
>> >> Subscription information may be found at:
>> >> http://www.groupstudy.com/list/CCIELab.html
>>
>>
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>>
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>>
>
>
> --
> Andrew Lee Lissitz
> all.from.nj_at_gmail.com
>

--
Andrew Lee Lissitz
all.from.nj_at_gmail.com
Blogs and organic groups at http://www.ccie.net