Cisco core switch CPU high

High CPU utilization on a Cisco core switch can be caused by network storms, misconfigured protocols, excessive logging, or specific processes like SISF, and can be mitigated through monitoring, process identification, and configuration adjustments.

Understanding High CPU Utilization

High CP

U usage occurs when the switch's processor is heavily engaged in tasks such as packet processing, routing protocol management (OSPF, BGP, EIGRP), ARP processing, ACL evaluation, and management traffic handling (SNMP, SSH, Telnet). While occasional spikes are normal—such as during topology changes or administrative commands—sustained CPU usage above 60–70% can indicate a problem and may lead to packet loss, increased latency, or network instability.

Common Causes

Network Storms: Broadcast, multicast, or unknown unicast storms can overload the CPU. Misconfigured Protocols: Spanning-tree loops, route flapping, or misconfigured routing protocols can generate excessive CPU load. Excessive Logging: Debugging or high logging levels can consume CPU resources.

Specific Processes: On Catalyst 9000 series, the Switch Integrated Security Features (SISF) process can spike CPU due to device tracking on trunk interfaces.

Software-

Switched Packets: Packets punted to the CPU instead of hardware forwarding can increase load.

Monitoring CPU Usage

Use the following commands to assess CPU utilization:show processes cpu history – Displays CPU usage over the last 60 seconds, 60 minutes, and 72 hours, helping identify spikes and trends.show platform health – Provides health metrics and can indicate if software-switched packets are contributing to high CPU.show processes cpu sorted – Lists processes by CPU consumption to pinpoint the culprit.

Mitigation Strategies

Identify and Limit High-CPU Processes: Determine which processes are consuming CPU and consider disabling or limiting them. For SISF-related spikes, disable device tracking on trunk interfaces or configure trusted ports and device roles to reduce unnecessary entries. Optimize Protocol Configurations: Ensure spanning-tree, routing protocols, and EtherChannel configurations are correct to prevent loops or flapping.

Reduce Logging Overhead: Avoid excessive debug or high-level logging in production environments. Offload Traffic to Hardware: Ensure that traffic is hardware-switched whenever possible to reduce CPU load.

Apply IO

S Commands: In some cases, commands like no ip redirects on uplink interfaces can significantly reduce CPU usage.

Key Takeaways

Occasional CP

U spikes are normal; sustained high usage requires investigation. Monitoring tools and commands help identify the root cause. Adjusting configurations, limiting high-CPU processes, and optimizing traffic handling can restore normal CPU levels and maintain network stability.