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Re: MST forwarding times CCO example confusing posted 11/02/2008
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Lol, I cached the train late and Petr already clarified the situation. :D



On Sun, Nov 2, 2008 at 9:42 PM, Huan Pham <pnhuan@xxxxxxxxx> wrote:

> Hi Cyrus,
>
> Thanks for your help.
>
> Assuming all switches in my scenario are running MST, did you mean that,
> there is no way we can force SW2 to wait a certain delay before turning
> backup root port into the forwarding state, in case the root port fails?
>
> Regards,
>
>
>
>
> --- On *Sun, 11/2/08, Cyrus <cyrus.mgh@xxxxxxxxx>* wrote:
>
> From: Cyrus <cyrus.mgh@xxxxxxxxx>
> Subject: Re: MST forwarding times CCO example confusing
> To: "Huan Pham" <pnhuan@xxxxxxxxx>
> Cc: "stephen skinner" <stephenski@xxxxxxxxx>, "shiran guez" <
> shiranp3@xxxxxxxxx>, "Cisco certification" <ccielab@xxxxxxxxxxxxxx>
> Date: Sunday, November 2, 2008, 9:32 PM
>
>
> Well, couple of things to considerate:
>
> 1- if all of bridges are in RSTP mode , there is no need of timers concept
> ,proposal/agreement mechanism would be used (Technically if u have p2p
> links,no 802.1D bridge and properly configured edge ports in your
> network).Timers concept is only used for 802.1D fallback.
>
> 2- MST use RSTP but "spanning-tree mst forward-time" only comes into
> consideration if at least 1 STP(802.1D) switch exist in network or in case
> of an indirect links (e.g. of non p2p links : switches connected to the
> hub!!)
>
> 3-When RSTP and STP wants to interoperate ,proposal/agreement mechanismcould not be used among them.So listening /learning timers come to play
>
> HTH,
>
>
>
> On Sun, Nov 2, 2008 at 8:08 PM, Huan Pham <pnhuan@xxxxxxxxx> wrote:
>
>>
>> Hi GS,
>>
>> Thanks Shiran for the clarification in the previous post.
>>
>> Switch(config)# spanning-tree mst forward-time 18
>>
>> Since MST uses rapid spanning tree by default, the command in discussion
>> only
>> changes the time it takes for a port from Disable to Forwarding (e.g. an
>> access port). Only those ports will go through that forwarding delay (if
>> port-fast is not enable), am I right?
>>
>> How about the backup root port, it will not need to go through this delay,
>> won't it?
>>
>> More specifically, let's have a simple topo, where SW1 is the root.
>>
>> SW1 ======== SW2 --------- SW3
>>
>> Both ports on SW1 are designated.
>> SW2 picks one of the ports (to SW1) as the root port. The other port is
>> backup
>> root (according to RSTP). Only the root port forward traffic from SW2 to
>> SW1.
>>
>> When the link with the root port fails, SW2 will automatically uses the
>> backup
>> root port to forward traffic, right?
>>
>> My questions are:
>>
>> - How we influence the delay to force SW2 wait 18 sec, before turning the
>> backup root port to be the root port (i.e. start forwarding traffic)?
>>
>> - Is there anyway we can disable RSTP within the MST?
>>
>> Thanks for your help.
>>
>> Huan
>>
>>
>> --- On Sun, 10/26/08, shiran guez <shiranp3@xxxxxxxxx> wrote:
>>
>> From: shiran guez <shiranp3@xxxxxxxxx>
>> Subject: Re: MST forwarding times CCO example confusing
>> To: "stephen skinner" <stephenski@xxxxxxxxx>
>> Cc: "Cisco certification" <ccielab@xxxxxxxxxxxxxx>
>> Date: Sunday, October 26, 2008, 6:30 PM
>>
>> The basic answer is no!
>>
>> the forward time is changing the FWD timer and that timer is used between
>> states, but the issue is when you use MST the default STP implementation
>> he
>> use is RSTP (Rapid STP -802.1w)
>>
>> meaning that the only states you will go is from learning to forwarding
>> that
>> mean that if you change the FWD timer this will be the time it take to
>> overall go to FWD state.
>>
>> I suggest you will read also to get a better understanding.
>>
>>
>> http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a008
>> 0094cfa.shtml
>>
>> the old implementation of STP 802.1d from 1998 is not used with MST.
>>
>> hope this helped you :-)
>>
>> On Sun, Oct 26, 2008 at 8:30 AM, stephen skinner
>> <stephenski@xxxxxxxxx>wrote:
>>
>> > hello,
>> >
>> > can i please ask a quick question ,
>> >
>> > i have been reading about the following command
>> >
>> > "spanning-tree mst forward-time"
>> >
>> > according to the CCO , it states
>> >
>> > The forwarding time specifies how long each of the listening and
>> learning
>> > states last before the interface begins forwarding.
>> >
>> > OK,
>> >
>> > but the example on the CCO shows this
>> >
>> > This example shows how to set the spanning-tree forwarding time to 18
>> > seconds for all MST instances:
>> >
>> > Switch(config)# spanning-tree mst forward-time 18
>> >
>> >
>> > my question is ,
>> >
>> > if the above statement about listening and forwarding states is correct
>> ,
>> > i.e this command covers the timer for both the listening and learning
>> > states
>> >
>> >
>> > then shouldnt the example have a forward time of 9 ??
>> >
>> >
>> > i beleive that they way you work out the forwarding time is as follows
>> >
>> > listening=9 and learning=9 ,  2x9 =18 in total.
>> >
>> > the example from the CCO would be
>> >
>> > listening=18 and learning=18 ,  2x18 = 36 in total.
>> >
>> > can someone please clarify this for me ...
>> >
>> > many thanks
>> >
>> >
>> > --
>> > Only two things are infinite, the universe and human stupidity, and
>> I'm not
>> > sure about the former.
>> >
>> >
>> > Blogs and organic groups at http://www.ccie.net
>> >
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>> >
>> >
>> >
>> >
>> >
>> >
>>
>>
>> --
>> Shiran Guez
>> MCSE CCNP NCE1 JNCIA-ER CCIE #20572
>> http://cciep3.blogspot.com
>> http://www.linkedin.com/in/cciep3
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
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>>
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>>
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>>
>
>
> --
> Sirus Moghadasian
> CCIE #21862 (R&S)
>
>


-- 
Sirus Moghadasian
CCIE #21862 (R&S)