Re: Spanning-tree detected flag

That seems to be correct!

On Wed, Sep 2, 2009 at 3:43 PM, Anantha Subramanian Natarajan <
anantha.natarajan_at_gravitant.com> wrote:

> Joe,
>
> Awesome and thank you very much.So just to confirm,the TC Deducted flag
> is not sent on the BPDU frame right ?
>
> Once again thanks
>
> Regards
> Anantha Subramanian Natarajan
>
> On Wed, Sep 2, 2009 at 11:25 AM, Joe Astorino <jastorino_at_ipexpert.com>wrote:
>
>> Check out the following link:
>> http://www.freepatentsonline.com/EP1330078.html
>>
>> "More specifically, upon detection of a change in the Spanning Tree,
>> switches transmit Topology Change Notification Protocol Data Unit (TCN-PDU)
>> frames toward the root. The TCN-PDU is propagated hop-by-hop until it
>> reaches the root which confirms receipt of the TCN-PDU by setting a Topology
>> Change Flag; additionally a TC flag can be set in BPDUs subsequently
>> transmitted by the root for a period of time. Other switches, receiving
>> these BPDUs, note that the Topology Change Flag has been set, thereby
>> alerting them to the change in the active topology."
>>
>> The way I read that is when a change happens, the TCN is sent up to the
>> root bridge. When the root bridge receives the TCN it acknowledges it by
>> setting the Topology Change Flag. When other bridges receive these frames,
>> they set their TC detected.
>>
>> On Wed, Sep 2, 2009 at 11:58 AM, Anantha Subramanian Natarajan <
>> anantha.natarajan_at_gravitant.com> wrote:
>>
>>> Hi All,
>>>
>>> When I was going through the "show spanning-tree active detail "
>>> command
>>> ,I noticed about the detected flag as pasted below (output truncated)
>>>
>>> VLAN0001 is executing the ieee compatible Spanning Tree protocol
>>> Bridge Identifier has priority 24576, sysid 1, address 0015.2b2c.f680
>>> Configured hello time 2, max age 20, forward delay 15
>>> We are the root of the spanning tree
>>> Topology change flag not set, *detected flag not set*
>>> **
>>> I was trying to understand,whether the detected flag is a seperate flag
>>> in
>>> 801.2d BPDU frame format or it just the switch sets for his purpose to
>>> understand that the TC notification has received from another switch with
>>> TC
>>> flag set.
>>>
>>> The way in which I understand the spanning-tree flags are
>>>
>>> 1) Its 1 byte in length
>>> 2) Only 2 bits are used for the flag
>>> 3) If the lower order bit is set (00000001),then its TC flag is set or if
>>> the high order bit is set (10000000),then it is TCA flag set.
>>>
>>> For some reason I couldn't understand the detected flag,Kindly help me to
>>> understand the same.I am sure missing some basic.
>>>
>>> Thanks for the help
>>>
>>> Regards
>>> Anantha Subramanian Natarajan
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>> --
>> Regards,
>>
>> Joe Astorino - CCIE #24347 R&S
>> Technical Instructor - IPexpert, Inc.
>> Cell: +1.586.212.6107
>> Fax: +1.810.454.0130
>> Mailto: jastorino_at_ipexpert.com
>>
>
>

-- 
Regards,
Joe Astorino - CCIE #24347 R&S
Technical Instructor - IPexpert, Inc.
Cell: +1.586.212.6107
Fax: +1.810.454.0130
Mailto:  jastorino_at_ipexpert.com
Blogs and organic groups at http://www.ccie.net