Re: Spanning-tree detected flag

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
>>
>>
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>
>
> --
> Regards,
>
> Joe Astorino - CCIE #24347 R&S
> Technical Instructor - IPexpert, Inc.
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Received on Wed Sep 02 2009 - 14:43:24 ART