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tihovsky
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Joined: Mon Aug 13, 2012 11:11 pm

High CPU use on switches

Wed Mar 29, 2023 11:37 pm

We have put in production a number of CRS354-48P-4S+2Q+RM for the edge layer. Each of them is connected between using QSFP links as some form of edge stacking.
Then we SFP+ from each "stack member" to the core layer consisting of a ring of 4 x CRS326-24S+2Q+RM forming a core loop interconnected through QSFPs.
So first edge "stack" member connects to cabinet 1 with 2x CRS326 and second edge "Stack" member connects to cabinet 2 with other 2x CRS326, etc. thus forming redundancy.
That's for L2 switching.

For L3 routing we use two VRRP-ed CCR1072 for each VLAN, each connected with LACP LAG formed out of 4x SFP+ towards two above mentioned CRS326 in the core cabinet..
So each router connects to two core switches located inside their cabinets with 4x SFP+ LACP.

Lots of VLANs, trunked and not ports and POE devices on the EDGE switches, with properly set bridge port path cost in a way that paths going towards the core switches and routers have less priority than QSFP connections in the edge.
Also Loop protection and higher RSTP cost is set activated for every edge port on the CRS354s to assure loops prevented as edge cannot be tightly controlled.

All works great for now, but sometimes attaching to 354s takes multiple tries with Winbox or through the Romon repetitively clicking on Connect until connected.
I also observe core and edge CPUs going anywhere between 11% and 100% for couple of seconds, although mostly staying below 30%, but CCRs are at 0-4% at most.
Switch CPU profiling tells me mostly management like 15-20% and then in smaller amount networking & bridging together like 10% consumes switch CPU (on the average).

Switching works fine, without noticeable latency introduced as a result of the above, but all this is starting to worry me as I don't know what to expect as we attach more client devices.

Do you have any recommendations or tips to avoid scaling issues with this config further into the project? It is an important project so I don't want to get surprised and stuck clueless.
Also not sure how to properly activate nor debug/log RSTP, so if you could help on that or some links covering the topic?
Hope not to cryptic in the explanation above.

Thx!

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