Why the CPU usage will be high when we configure many vlanif interfaces?


When a VLANIF interface is configured on the S3700 / S5700EI switch, the switch sends an ACL to capture ARP packets from the VLAN to the control plane. When the configured VLANIF interface is too large (more than 8 for S3700s and more than 32 for S5700EIs), the switch sends an ACL to capture ARP packets from all VLANs to the control plane for software forwarding due to ACL resource restrictions. The ACL will also capture Layer 2 ARP packets from VLANs that are not VLANIF interfaces. If the number of ARP packets forwarded by Layer 2 packets is high, the ACL will be overloaded and the CPU occupancy rate will be too high.

For the S2752 / S3700 series switches, it is not recommended to configure more VLANIF interfaces due to specifications and hardware performance. In order to avoid excessive ARP and ARP-Miss packets, CPU usage is too high. It is recommended to configure the arp-fake expire-time 30 in each VLANIF interface view to optimize the ARP entries to reduce CPU usage and recommend the latest patches.

Other related questions:
Why is the CPU usage high when VLANs are created or deleted through GVRP in default configuration
The switch supports VLAN configuration on devices at both ends. When GVRP is enabled on the network, it advertises information about dynamic VLANs in two directions. Then the intermediate devices dynamically create and delete VLANs based on the information. Dynamic maintenance of VLANs can greatly reduce manual configurations. The maximum 4 K dynamic VLANs are frequently created and deleted, which triggers larger amount of packet communication. Receiving packets and delivering dynamic VLANs occupy large amount of CPU resources. In actual networking, you need to adjust GARP timers to the recommended values. NOTE: The recommended values of the GARP timers are as follows: GARP Hold timer: 100 centiseconds (1 second) GARP Join timer: 600 centiseconds (6 seconds) GARP Leave timer: 3000 centiseconds (30 seconds) GARP LeaveAll timer: 12,000 centiseconds (2 minutes) When more than 100 dynamic VLANs are created, use the preceding recommended values. When the number of dynamic VLANs increases, lengths of the GARP timers need to be increased.

CPU usage of the AR3260 is too high
The reason why the CPU usage of the AR3260 is high may be that the AR is attacked, which can be identified as follows: 1. Run the display snmp-agent statistics command to view SNMP statistics, and check whether the number of SNMP packets received on the AR exceeds the queue buffer and some packets cannot be processed. 2. Capture packets to check whether the AR is attacked. For details, see CPU Usage of an AR3260 Is Too High.

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