User manual

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ES-2000 Series
9 RATE LIMIT CONFIGURATION
Use the Traffic > Rate Limit page to apply rate limiting to ingress or egress
ports. This function allows the network manager to control the maximum
rate for traffic received or transmitted on an interface. Rate limiting is
configured on interfaces at the edge of a network to limit traffic into or out
of the network. Packets that exceed the acceptable amount of traffic are
dropped.
Rate limiting can be applied to individual ports. When an interface is
configured with this feature, the traffic rate will be monitored by the
hardware to verify conformity. Non-conforming traffic is dropped,
conforming traffic is forwarded without any changes.
COMMAND USAGE
The ASIC used to control the ingress rate limit has a default time frame
of 1 ms, 10 ms, 100 ms, and 1 second respectively for 10 Gbps, 1 Gbps,
100 Mbps, and 10 Mbps connection rates. Ingress rate limiting is processed
100 times per second (also referred to as 100 scales per second),
regardless of the packet size.
N OTE : Egress rate limiting does not function in this manner.
For example, a Gigabit port has a 10 ms window size, so there are 100
scales per second, each scale having a bandwidth of 10 Mbps, and using an
inter-packet gap of 20 bytes.
Therefore, when the rate limit is set at 64 kbit/s, each scale has a shared
bandwidth of 80 bytes.
When the packet size = 64 bytes, and the gap = 20 bytes,
each packet = 84 bytes > 80bytes. Only one packet can pass through in
each scale. One second has 100 scales, so the rate is 100 packets per
second.
When the packet size = 640 bytes, and the gap = 20 bytes,
each packet = 660 bytes > 80 bytes. The switch will only let one packet
pass in each scale, so there are still 100 packets per second.
When the packet size = 1500 bytes, and the gap = 20 bytes,
each packet = 1520 bytes > 80 bytes. The switch will only let one packet
pass in each scale, so there are still 100 packets per second.
The following table shows the actual number of packets received when
various ingress rate limits are applied to packets of different sizes. The
values shown below were measured for both ingress rate limiting and
storm control functions.