Port-Based Fixed Rate Limiting

You can configure a fixed rate limiting policy on a port in the inbound direction only. This feature allows you to specify the maximum number of bytes in kilobits per second (kbps) a given port can receive. The port drops bytes that exceed the limit you specify.

Fixed rate limiting applies to all traffic on the rate-limited port. It counts the number of bytes that a port receives in one second intervals. If the number of bytes exceeds the maximum number you specified when you configured the rate, the port drops all further inbound packets for the duration of the one-second interval. Unused bandwidth is not carried over from one interval to the next. Once the one-second interval is complete, the port clears the counter and re-enables traffic.

Note: RUCKUS recommends that you do not use fixed rate limiting on ports that receive route control traffic or Spanning Tree Protocol (STP) control traffic. If the port drops control packets due to the Fixed rate limiting policy, routing or STP can be disrupted.

When you specify the maximum number of bytes, you specify it in kilobits per second (kbps). The fixed rate limiting policy applies to one-second intervals and allows the port to receive the number of bytes you specify in the policy but drops additional bytes. Unused bandwidth is not carried over from one interval to the next.

Unused bandwidth can be used to consume bursts in traffic. When a group of packets which has shorter inter-packet gaps comes in, a higher bandwidth is required to consume these bursts. This additional bandwidth is borrowed from unused bandwidth in a set interval.

Each device supports line-rate rate limiting in hardware. The device creates entries in Content Addressable Memory (CAM) for the rate limiting policies. CAM entries enable the device to perform the rate limiting in hardware instead of sending the traffic to the CPU. The device sends the first packet in a given traffic flow to the CPU, which creates a CAM entry for the traffic flow. A CAM entry consists of the source and destination addresses of the traffic. The device uses the CAM entry for rate limiting all the traffic within the same flow. A rate limiting CAM entry remains in the CAM for two minutes before aging out.

Note: CPU traffic can also be rate-limited by applying traffic policies using ACLs. Refer to Applying ACLs to rate limit inbound CPU traffic.
Parent topic: Port-Based Fixed Rate Limiting Configuration Notes