From: Cyrus (cyrus.mgh@gmail.com)
Date: Sun Nov 02 2008 - 08:32:49 ARST
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@yahoo.com> 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@gmail.com> wrote:
>
> From: shiran guez <shiranp3@gmail.com>
> Subject: Re: MST forwarding times CCO example confusing
> To: "stephen skinner" <stephenski@gmail.com>
> Cc: "Cisco certification" <ccielab@groupstudy.com>
> 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<http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.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@gmail.com>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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>
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