11-28-2012 02:37 PM - edited 03-07-2019 10:17 AM
Hi Everyone.
On Flat Layer 2 Network if distribution switch is 3750 and it is stack of 2 switches.
Currently it has only 1 uplink to core switch.
If i config another uplink to core switch for redudancy it will be in STP blocking state right as this is default behaviour right?
Also if i config both uplink ports in layer 2 etherchannel bundle and they go to same core switch will then both ports will be in
forwarding state?
My understanding is that in etherchannel they do load balance so if both ports are in forwarding state will it cause STP issues
with core switch like loop?
Is there any advantage of config uplink ports as Layer2 etherchannel ?
Thanks
Mahesh
Solved! Go to Solution.
11-28-2012 03:10 PM
Hi Mahesh,
If i config another uplink to core switch for redudancy it will be in STP blocking state right as this is default behaviour right?
Correct,
Also if i config both uplink ports in layer 2 etherchannel bundle and they go to same core switch will then both ports will be in forwarding state?
Correct
If you add a second link, put them both in an Etherchannel, so there is no blocking and since the 3750 by default utilizes source-destination-mac, it will load balance the traffic from different sources to the links in the portchannel
My understanding is that in etherchannel they do load balance so if both ports are in forwarding state will it cause STP issues with core switch like loop?
No, there will be no STP since both ports are in an Etherchannel and they are logically one link.
Is there any advantage of config uplink ports as Layer2 etherchannel ?
Yes, as I mentioned above, load balancing and no STP.
HTH
Reza
11-29-2012 10:37 AM
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
No, there will be no STP since both ports are in an Etherchannel and they are logically one link.
Just to clarify what Reza described, generally STP is active on Etherchannel too, but as Reza also notes, it's treated at a single link. I.e. is doesn't block or not the individual Etherchannel links, but it could block or not the whole logical Etherchannel.
For example, the Etherchannel link can block or not if there's another L2 path (which could also be another Etherchannel).
11-28-2012 03:10 PM
Hi Mahesh,
If i config another uplink to core switch for redudancy it will be in STP blocking state right as this is default behaviour right?
Correct,
Also if i config both uplink ports in layer 2 etherchannel bundle and they go to same core switch will then both ports will be in forwarding state?
Correct
If you add a second link, put them both in an Etherchannel, so there is no blocking and since the 3750 by default utilizes source-destination-mac, it will load balance the traffic from different sources to the links in the portchannel
My understanding is that in etherchannel they do load balance so if both ports are in forwarding state will it cause STP issues with core switch like loop?
No, there will be no STP since both ports are in an Etherchannel and they are logically one link.
Is there any advantage of config uplink ports as Layer2 etherchannel ?
Yes, as I mentioned above, load balancing and no STP.
HTH
Reza
11-29-2012 07:42 AM
Hi Reza,
Many thanks again.
Regards
Mahesh
11-29-2012 10:37 AM
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
No, there will be no STP since both ports are in an Etherchannel and they are logically one link.
Just to clarify what Reza described, generally STP is active on Etherchannel too, but as Reza also notes, it's treated at a single link. I.e. is doesn't block or not the individual Etherchannel links, but it could block or not the whole logical Etherchannel.
For example, the Etherchannel link can block or not if there's another L2 path (which could also be another Etherchannel).
11-29-2012 10:59 AM
Hi Joseph,
Thanks for adding very useful into to the post.
Regards
Mahesh
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