Thursday, December 6, 2018

Impact of changing STP prioirity and bringing a redundant link online

There's two related network changes I'll be making soon and I want to understand if they'll cause any network disruption.

The first is just changing the STP priority on a switch (S1) running RSTP. It currently has a prioirity of 40960 and I need to change it to 61440. It's connected to a core switch/router (R1) running MSTP, with priority 12228, and all the core switches in the network have priorities in the range 0-32768.

As the priority value is higher than any upstream switch, and will remain so after I change it, am I right in thinking that this should be entirely non-disruptive, or might there be a STP recalculation or reconvergence with some associated disruption to forwarding?


The second change is to make a redundant link from S1 to a second switch (S2) which will in turn connect to a different core switch (R2) which is in another DC. S2 will be running MSTP with a priority of 40960, and again, all upstream core switches have a lower priority value.

The intention is that the redundant link will immediately be blocked on S1, coming online if S1 loses its connection to R1.

Would you expect any interruption to forwarding on S1 when the redundant link comes online, or any disruption upstream?



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