Re: question on port fast and bpdu guard

LOL!!! I'll take that over getting the job and working with a bunch of
people that don't know what the hell they are talking about : ) I've
been there and done that and it is not nearly as much fun hehe

On Thu, Apr 15, 2010 at 2:56 PM, Jack Router <pan.router_at_gmail.com> wrote:
> After the interview you receive a polite email that you are overqualified
> for the position :)
>
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Joe
> Astorino
> Sent: 15-Apr-10 14:25
> To: imran ali
> Cc: cristian.matei_at_datanets.ro; Cisco certification
> Subject: Re: question on port fast and bpdu guard
>
> To put it simply, because they would have an interface that after STP
> convergence was not either a root port (RP) or designated port (DP)
> and therefore, the STP algorithm places those interfaces in a blocked
> state. If it was my interview I would have asked who the root bridge
> in the topology was so that I could draw out exactly the state of each
> port.
>
> Let's assume SWA is the root bridge. Links would have these states:
>
> SWA/SWB Link: DP
> SWA/SWC Link: DP
>
> SWB/SWA Link: RP
> SWC/SWA Link: RP
>
> Now what happens next would depend on some things....for SWD to choose
> a root port it will pick the interface with the lowest cost path to
> the root bridge. In our topology we will say all links are equal.
> Therefore, SWD has two equal cost patch to the root, so it will
> evaluate lowest sending BID. Let's say SWB has the lower BID here. So
> then...
>
> SWB/SWD Link: DP
> SWD/SWB Link: RP
>
> SWC/SWD Link: DP
> SWD/SWC Link: BLOCKING <--- not root or designated.
>
> P.S. the blocking link KNOWS it is not the DP due to the information
> sent in the BPDU's on the segment in this case from SWC. SWC has a
> superior BPDU and wins the day for the right to be DP on that segment
>
> HTH!
>
> On Thu, Apr 15, 2010 at 12:18 PM, imran ali <immrccie_at_gmail.com> wrote:
>> Thanks you Anthony & Cristian,
>>
>> i have the following topology
>>
>> SWA--------------------------------------------SWB
>> | |
>> | |
>> | |
>> | |
>> | |
>> SWC--------------------------------------------SWD
>>
>>
>> IS there a loop in the network.?? yes as each switch has tow different
> paths
>> to reach the other switch ..
>>
>> *how does SWC or SWD know about the loop in the topology ..*
>>
>> This was my interview question...i simply said " by examining BPDU'S.."
> but
>> he needed more detailed answers..
>>
>> i am looking for more technical answer..
>>
>> Thanks
>>
>> On Thu, Apr 15, 2010 at 8:56 PM, Cristian Matei
>> <cristian.matei_at_datanets.ro>wrote:
>>
>>> Hi Ali,
>>>
>>> BPDU Guard and BPDU Filter can be applied in the following 2 ways:
>>> -at the global level; once enabled here it will get
> applied
>>> only to PORTFAST enabled ports (I say enabled and not configured as a
>>> configured portfast port may lose its portfast status in certain
>>> conditions)
>>> -at the interface level; once enabled here it's just
> applied
>>> regardless of the portfast status of the port (so portfast is not
> required
>>> in this case)
>>>
>>> Now PORTFast itself is not "needed" for STP or RSTP; it just improves
>>> end-to-end STP/RSTP convergence time; for best end-to-end convergence
> time,
>>> PORTFAST is required to be explicitly configured in both STP and RSTP.
>>>
>>> Regards,
>>> Cristian.
>>>
>>> -----Original Message-----
>>> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
>>> imran ali
>>> Sent: Thursday, April 15, 2010 5:49 PM
>>> To: Cisco certification
>>> Subject: question on port fast and bpdu guard
>>>
>>> HI gurus,
>>>
>>> does enabling bpdu guard requires a port fast to be enabled.. i mean
> bpdu
>>> guard can be enabled independent of port fast status ?.
>>>
>>> further why portfast is required in traditional STP topology and not in
>>> RSTP
>>> networks..??
>>>
>>> can i enable portfast feature in RSTP netorks
>>>
>>> Thanks,
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
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>>
>>
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>>
>>
>>
>>
>>
>
>
>
> --
> Regards,
>
>
>
> Joe Astorino - CCIE #24347
> Sr. Technical Instructor - IPexpert
> Mailto: jastorino_at_ipexpert.com
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-- 
Regards,
Joe Astorino - CCIE #24347
Sr. Technical Instructor - IPexpert
Mailto: jastorino_at_ipexpert.com
Telephone: +1.810.326.1444
Live Assistance, Please visit: www.ipexpert.com/chat
eFax: +1.810.454.0130
IPexpert is a premier provider of Self-Study Workbooks, Video on
Demand, Audio Tools, Online Hardware Rental and Classroom Training for
the Cisco CCIE (R&S, Voice, Security & Service Provider)
certification(s) with training locations throughout the United States,
Europe, South Asia and Australia. Be sure to visit our online
communities at www.ipexpert.com/communities and our public website at
www.ipexpert.com
Blogs and organic groups at http://www.ccie.net