Connecting a Port channel

[sasanka1912]

Hi ,

we have two core switches namely CORE 1(rstp root bridge)  AND CORE 2 connecting to our SD-WAN platform via SDWAN-1 and SDWAN 2.Now we have another 3 switches (SW1,SW2 AND SW3) Connecting to both core 1 and core 2 but not SW4. SW4 Connecting to Core 2 and all Core and SW switches configured as transparent mode.Now i am planning to configure a port channel and connect sw4 ----->CORE1 so that it will complete the layer 2 ring and resilience.

My question is : The moment i bring the port channel up , will there be any RSTP calculation and impact any services ?

please advise 

[Jan Rolny]

Hi sasanka1912,

diagram how switches are connected would be useful. It's not clear and you say something about the "ring" it's more unclear. 

Spanning-tree can always disrupt communication if it is wrongly configured. So first ensure you have correct priority configured on SW4 so it will not take over root bridge role. 

Next are you adding SW4 to current port-channel or new one?  

There is always some STP recalculation when you connect new switch to the network, but if properly configured it will just connect and will not cause any service disruption.

Best regards,

Jan

[sasanka1912]

@Jan Rolny All the switches configured as transparent mode and  correct priorities configured on root bridge.

Now the port channel that I will be configuring, will be a new port channel  between sw4----core1(root bridge) and all switches configured with rstp.

Once the new port channel open up, my understanding will be rstp recalculate and block certain ports based on the calculation and duration will depends how soon it receive the acknowledgement for it's proposal.(but should it recalculate the core switch where it is the root) 

I will attach a diagram soon, and thanks for your reply

[Jan Rolny]

Hi sasanka1912,

as I said it depends on your topology. If every switch is connected to the core independently (ie. like star topology) and STP priorities are properly setup so then no disruption will happen. New switch will connect, establish new ether channel and be part of your STP.

Hope this helps.

Jan