ExtremeSwitching (EXOS)

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 Stack link blocking election

jpb's profile image
jpb posted 05-12-2022 09:30
I have a stack in a ring topology with 5 x460g2-48t-4ge10 and the link between stack-ports 3:2 and 4:1 looks to be bad. I have already changed cables, etc to bring it down to being just one of the ports flapping. I have rearranged the stack to go 1-2-3-5-4 rather than 1-2-3-4-5 so I will soon see if 3:2 or 4:1 is the problem. The blocked port is between 2:2 and 3:1 and I would like to move it to the 3:2 to 4:1 link.  I have been unable to find anything about how the blocked stacking link is elected or how to affect it. Switch 1 in this stack is the master and is the only one set as master capable. 

Q: How does a homogenous ring switch stack elect the blocking port/link? Can this be changed and if so how?
Gabriel_G's profile image


Generally I've seen that the blocked stack port is between slot 1 port 2 and slot 2 port 1, although having a link down or 'no-neighbor' in 'show stacking stack-ports' may affect this behavior.

Checking in the EXOS User Guide, I see no reference of how this stack-port is determined, and I see/know of no way to manipulate this behavior.

Note that the 'blocking' only blocks Broadcast, Multicast, and Unknown Unicast flooding. Normal Unicast traffic still traverses the blocked stack port to use the shortest path to the destination slot. Ultimately, which port is blocked shouldn't have an significant impact on stack behavior, although a flaky link can cause stack-instability depending on location.

Hopefully that helps!

Adrian Orellana's profile image
Adrian Orellana
I would try to reboot the 3rd slot so when it comes up the other stack ports are in the control path and maybe you can achieve 3:2-4:1 bloked