05-31-2010 02:02 AM - edited 03-06-2019 11:20 AM
Hi
I would like to know why stp just sends bpdu over the first interface in an etherchannel not others ?
Thanks.
05-31-2010 02:06 AM
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
05-31-2010 02:15 AM
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.
05-31-2010 02:26 AM
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
06-01-2010 12:03 AM
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)
Hope to Help !!
Ganesh.H
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