Hey need advise. I tried to simulate this in CML, but I couldn’t get what I wanted.
I need to replace the two Old-Switch 1 and Old Switch 2 in attached file with new Cisco model. Just trying to understand how many time of disruptions I would likely get when doing the replacement. (I am using ping from PC1 to PC2 to simulate traffic) Below are the sequence orders I plan to do. BTW I can only swap out 1 Switch at a time.
Lower Router 1 HSRP priority, Router 2 would be active Router. Then swap out Old-Switch 1 first, I think 1 disruption of about a min due to STP convergence?
New Switch 1 would become root bridge (we set priority to 0)
Connect New-Switch 1 to Old-Switch 2, 1 more disruption abt 1 min due to STP convergence?
Connect Switch 3 to New Switch 1. No STP here.
Connect New Switch 1 to Router-1, I don’t expect disruption
Remove Old Switch 2 and replace it with New Switch 2. Connect New Switch 2 to New Switch 1, follow by connect New Switch 2 to Switch 4 then to Router-2. I don’t think disruption here since all traffic would be by handled by New- Switch 1 and New Switch 1 the root bridge.
Is my understanding correct? I would manipulate the HSRP priority accordingly when doing eqpt swap. Any advise would be good. Thanks
At first glance, your process looks good. I assume that the new switches going in will be functioning exactly the same as those coming out. If your configs are correct, you should have no problem. Assuming you’re running Rapid STP your downtime should be a matter of seconds. Also, changing the priority on the HSRP routers is a good idea too.
Thanks Laz. I afraid it would be a mixture of Rapid STP and PVST within this setup.
My network is on Rapid and cliend end likely PVST. I read another of thread on how fast the convergence like when there’s a change occurs in a link, assume default values for timers.
If I understanding correctly, my guess is since I’m to remove the root bridge first (Old Switch-1), a new root would need to be elected, likely Old Switch 2 would take over and root has to be reelected again when I put in the new Switch-1 (as priority is set to 0), so at least two disruptions I would see for not more than 1 mins each when I replace Switch 1. Once the New Switch-1 is in place, all traffic should flow thru Switch-3, New-Switch-1 to Router-1 (Active HSRP) to PC1.
When replacing Old-Switch-2, I think likely there would be again 2 disruptions again, one is 6-10 seconds disruption (Rapid STP between these Switch-1 and 2) and another one when connecting Switch-4 to New Switch-2, this may be 1 mins (as client side running PVST and my end Rapid). Unless I time the the cable move between Switch-1 and 2 and Switch-2 to Switch 4 together, then I may be able to cut down disruption to just 1 instead of 2.
So total 4 disruptions I would have to expect as minimum (or more realistic), correct me if I’m wrong about this disruption due to STP convergence. Thanks again.
To start with, you can make Old Switch 2 root bridge by changing priorities. You can do that during off-hours, maybe at night, so that there will be no disruption. That way, when you remove Old Switch 1, there will be no reconvergence. This way you can eliminate one disruption, or at least initiate it during a low usage time.
But I think the rest of your description makes sense and so does being prepared for 4 disruptions. I hope your migration goes well, let us know how you get along.
