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Spanning Tree Config + Full Mesh LAG
I've created a full mesh LAG between 2 switch stacks (stack 1&2, then stack switches 3&4) as shown in the basic diagram below. The top stack is a pair of PC 6224s and the bottom are a pair of PC 80244F switches. There are 4 cables, so that each switch is connected to all other switches directly over a stacking cable (shown by thick line) or an ethernet cable. These 4 cables make up a single LAG - port channel 1.
After running show spanning tree command, I've noticed that the port channel on the root switch (port channel 1) has a cost of 5000. On switches 1 & 2 the STP costs match up OK, but I'm wondering whether it's worth changing the STP cost of port channel 1 on switch 3. Because switch 3 is a 10Gbps switch with some 1 Gbps ehternet ports, the 10 Gbps distribution ports to my servers have a cost of 2000. I'm wondering whether I should re-configure the port channel cost to say 1000 to avoid any network or RSTP issues down the line. Having said that, the 10Gbps ports do not directly plug into any other switches.
Pleas advise.
Thanks
DELL-Josh Cr
Community Manager
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Posted October 21st, 2013 08:00
Hi,
With the switches being stacked the 6024 stack has to be able to reach root through the LAGs to the 8024F stack and will connect to root to be even be able to see the 10Gb ports, so it isn’t going to use the 10Gb ports even if they have a lower cost. If you were planning on adding additional layers of 10Gb switches it might matter, but the current topology it should work fine as is.
If you run show spanning-tree active we can see which ports it is using currently.