Issue
The Cisco CSS is showing a high level of CPU usage, even though the networking throughput does not appear excessively high nor is there a large number of EQL or DQL`s configured.
CSS11501# sh system-resources cpu
Chassis CPU Utilizations
Module Name Module 5Sec 1Min 5Min
—————————————————-
CSS501-SCM-INT 1 90% 88% 75%
CSS501-SSL-C-INT 2 0% 0% 0%
Solution
Though there can be a number of causes to high CPU, within this article we look at the CPU resource consumption being due to the flow table.
Due to a high level of connections transversing the CSS the LoadBalancer uses CPU resource to build the subsequent flows within the flow table.
This can be confirmed using the following command and viewing the hit counters :
CSS11501# sh flow-state-table
Flow-Disable Timeout: 5
Port Protocol NAT-State Flow-State Hit-Count
————————————————————
53 TCP ——— flow-enable 6228 *
53 UDP ——— flow-enable 6399259 *
67 TCP ——— flow-disable 20 *
67 UDP nat-disable flow-disable 0 *
68 TCP ——— flow-disable 103 *
68 UDP nat-disable flow-disable 0 *
137 TCP ——— flow-disable 19 *
137 UDP nat-disable flow-disable 112690 *
138 TCP ——— flow-disable 71 *
138 UDP nat-disable flow-disable 0 *
161 TCP ——— flow-disable 13 *
161 UDP nat-disable flow-disable 164570 *
162 TCP ——— flow-disable 35 *
162 UDP nat-disable flow-disable 0 *
520 UDP nat-disable flow-disable 0 *
5060 UDP ——— flow-enable 88 *
8089 UDP nat-disable flow-disable 12 *
In this instance we could see a large increase in the DNS hit counters, based on this the flow state was disabled for UDP/53, and the CPU utilization returned to an acceptable level.
flow-state 53 udp flow-disable nat-enable
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