Brocade TurboIron 24X Series Configuration Guide - Manual (Page 1064)

1030 Brocade TurboIron 24X Series Configuration Guide
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Rate limiting in hardware
How Fixed Rate Limiting works
Fixed Rate Limiting counts the number of kilobits that a port receives, in one second intervals. If
the number exceeds the maximum number you specify when you configure the rate, the port drops
all further inbound packets for the duration of the one-second interval.
Once the one-second interval is complete, the port clears the counter and re-enables traffic.
Figure 126 shows an example of how Fixed Rate Limiting works. In this example, a Fixed Rate
Limiting policy is applied to a port to limit the inbound traffic to 500000 bits (62500 bytes) a
second. During the first two one-second intervals, the port receives less than 500000 bits in each
interval. However, the port receives more than 500000 bits during the third and fourth one-second
intervals, and consequently drops the excess traffic.
FIGURE 126 Fixed Rate Limiting
NOTE
The software counts the kilobits by polling statistics counters for the port every 100 milliseconds,
which provides 10 readings each second. Due to the polling interval, the Fixed Rate Limiting policy
has an accuracy of within 10% of the port's line rate. It is therefore possible for the policy to
sometimes allow more traffic than the limit you specify, but the extra traffic is never more than 10%
of the port's line rate.
Configuration notes
• Rate limiting is available only on inbound ports.
• Priority-based rate limiting is not supported on TurboIron devices.
• Fixed rate limiting is supported on GbE and 10 GbE ports.
• Fixed rate limiting is not supported on tagged ports in the base Layer 3 and full Layer 3 images
• The rate limit on IPv6 hardware takes several seconds to take effect at higher configured rate
limit values. For example, if the configured rate limit is 750 Mbps, line-rate limiting could take
up to 43 seconds to take effect.
Zero bps
Beginning of
one-second
interval
500000 bps (62500 bytes)
The Fixed Rate Limiting policy
allows up to 500000 bits
(62500 bytes) of inbound traffic
during each one-second interval. Once the maximum rate is reached,
all additional traffic within the
one-second interval is dropped.
One-second
interval
One-second
interval
One-second
interval
One-second
interval