Re: Portfast Clarification

Hey team,

I am coming into this a bit late ... pardon the late showing please.

Optional STP features link:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_se/configuration/guide/swstpopt.html

Personally, I find the Catalyst docs to be fairly good for our studies and
all around engineer efforts. Please see the link above for a good
explanation of the features mentioned.

When you configure these additional options, I might suggest you check this
command for your labs:

show spanning-tree interface ..xyz.. detail

This will give you some insight as to what is occurring per interface.
Also, @ the end of the link I provided you will see some additional show
commands which might help.

Have a great night,

Andrew Lee Lissitz

On Tue, Dec 1, 2009 at 1:57 AM, Babatunde Sanda <sbabatunde1_at_ca.rr.com>wrote:

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