RE: Portfast Clarification

Sarad,

The spanning portfast just lets the port transition directly into forwarding
state.

-----Original Message-----
From: Babatunde Sanda [mailto:sbabatunde1_at_ca.rr.com]
Sent: Monday, November 30, 2009 10:48 PM
To: 'Sarad'
Cc: 'Cisco certification'
Subject: RE: Portfast Clarification

Yes you are right. Even though the port is configured for portfast this
only stops the port from going through the spanning tree states listening,
learning forwarding and blocking Depending on what spanning tree process you
have configured. Eventually the loop will be detected and acted upon by the
switch.

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Sarad
Sent: Monday, November 30, 2009 10:20 PM
To: Babatunde Sanda
Cc: Cisco certification
Subject: Re: Portfast Clarification

Hi Sanda,

Thanks for your reply

It's clear how BPDU gurd works,

The next observation I would like to clarify is even though I enable
Portfast on all the links it will create only tempory links isn't it? Switch
detects loops after a few seconds & run stp to block loops. When we enable
portfast switch warning message also include the same thing as follows,

portfast should only be enabled on ports connected to a single
 host. Connecting hubs, concentrators, switches, bridges, etc... to this
 interface when portfast is enabled, can cause temporary bridging loops.
 Use with CAUTION

Rgds
Sara

On Tue, Dec 1, 2009 at 11:37 AM, Babatunde Sanda
<sbabatunde1_at_ca.rr.com>wrote:

> Sarah don't let the terms confuse you. When you use the command
> "spanning-tree guard root" on a port (which ideally is to be used on a
root
> bridge) you are protecting the election of the root bridge. When you use
> the command "spanning-tree bpdu enable" on a portfast interface or you use
> the global command spanning-tree bpdu default, this will prevent bpdu
> traffic from being carried on a portfast enabled port. In otherwords it
is
> used to prevent loop when a brigde / switch is plugged into a portfast
> enabled interface. I think the port will go into an inconsistent state.
>
> Example:
> I have 3 switches plugged together. I elect one of them as my root and
> place the command "spanning-tree guard root" where the other two plug into
> my elected root. This will not let any of the other 2 switches overthrow
> my
> elected root switch even if they have lower bpdu id.
>
> Now on any of the other two I intend plugging pc's so I configure the
ports
> as portfast and place the command "spanning-tree bpdu enable" on the
ports.
> Some guy from space comes and removes the pc and plugs a switch. As soon
as
> he does that the port transitions into "inconsistent state" (if you do
"sho
> int status" you will see this state). This will prevent that plugged
switch
> from causing a loop on my network.
>
>
>
>
>
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Sarad
> Sent: Monday, November 30, 2009 9:39 PM
> To: Babatunde Sanda
> Cc: Cisco certification
> Subject: Re: Portfast Clarification
>
> Hi Sanda,
>
> Is it Root guard or BPDU gurd which used on a root brigde to protect it
> from
> being overthrown by a switch with lower root id. ?
>
> The other observation is even though I enable the portfast I noticed that
> it
> runs STP once it detect a loop.
>
> Thanks
>
> Sara
>
>
> On Tue, Dec 1, 2009 at 11:04 AM, Babatunde Sanda
> <sbabatunde1_at_ca.rr.com>wrote:
>
> >
> >
> > Portfast disables spanning-tree. Bpdu-guard is used on a root brigde to
> > protect it from being overthrown by a switch with lower root id. Bpdu
> filter
> > will listen for bpdu trafic on the ports it's configured and drop it.
> Your
> > number 1 observation is right. This features are not enabled
> automatically
> > after enabling portfast.
> >
> > Observation 2. Since portfast disables spanning tree, a switch plugged
> into
> > such port runs the risk of loop because it doesn't know where to "fall"
> the
> > tree. And this ports will stay the way they are until you intervain by
> > changing the port state.
> >
> >
> > Sent from my Iphone.
> >
> > On Nov 30, 2009, at 9:10 PM, Sarad <tosara_at_gmail.com> wrote:
> >
> > Hi Experts,
> >>
> >> I have created some labs on stp portfast & had some observations. I
> would
> >> like to verify whether my observations are correct with you all. My
> >> observations are as follows.
> >>
> >>
> >> 1. If I enable portfast default on the switch or portfast on a
> >> particular
> >> interface will BPDU filter or BPDU gurad get enable by default
> >> (irrespective
> >> of trunk or access port)?My observation is no
> >>
> >>
> >> 2. If not it will create a temporary loop on the network if there are
> >> switches configured on the ports with portfast enable but after few
> >> seconds
> >> stp will run on those ports & move those ports to forwarding or
blocking
> >> stage.
> >>
> >> Thank you in advance
> >>
> >> Sara
> >>
> >>
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> >>
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Received on Mon Nov 30 2009 - 22:57:01 ART