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Etherchannel Bpdu

Hi

I would like to know why stp  just sends bpdu over the first interface in  an etherchannel not others ?

Thanks.

4 REPLIES
Hall of Fame Super Silver

Re: Etherchannel Bpdu

Hello Manie,

STP treats the etherchannel as a single logical link, as a result of this only one BPDU is sent and only out one member link as a result of load sharing rules for non IP frames.

Other protocols like LACP can deal with checking health of single member links and are recommended for this reason

Hope to help

Giuseppe

Community Member

Re: Etherchannel Bpdu

Thank you so much or your answer, but I would like to know

why it sends bpdu out of first physical interface ? and how can I verify that , I mean is there any command that shows me what interface the bpdu is sent out it ?

thanks.

Hall of Fame Super Silver

Re: Etherchannel Bpdu

Hello Manie,

you could check this with   a detailed debug command like:

debug spanning-tree bpdu ?

  receive   Received spanning tree (non-optimized path)

>>  transmit  Transmitted spanning tree BPDU (non-optimized path)

 

CAUTION: doing this in a production network can cause extended out of service making the switch not working and not manageable.

So consider this option only in a lab environment.

From the point of view of the bundle BPDUs could be sent out every member link but probably only one is used as a result of

load balancing based on MAC DA exor MAC SA

for BPDU MAC destination address is a multicast address (multiple values are possible depending if the link is a L2 trunk or not)

BPDU MAC source addres is the source MAC address, in this case it should be the MAC address associated to the bundle.

Hope to help

Giuseppe

Re: Etherchannel Bpdu

Thank you so much or your answer, but I would like to know

why it sends bpdu out of first physical interface ? and how can I verify that , I mean is there any command that shows me what interface the bpdu is sent out it ?

thanks.

Hi,

Check out the below link for debug spanning tree in switches and As Giuseppe told using these command can be problem in production network so before using these command just check the usage in network and use in off peak hours, debug spanning-tree bpdu privileged EXEC command to enable debugging of sent and received spanning-tree bridge protocol data units (BPDUs)

http://www9.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_20_ea2/command/reference/debug.html#wp1030122

Hope to Help !!

Ganesh.H

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