Configuration Guide User guide
FastIron Configuration Guide 1949
53-1002494-02
Rate limiting in hardware
NOTE
The software counts the bytes 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 for rate limiting
• Rate limiting is available only on inbound ports.
• Port based Rate limiting is not supported on the SX-FI62XG and SX-FI42XG modules of the
FastIron X Series devices.
• FastIron X Series devices do not support fixed rate limiting 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.
Configuring a port-based rate limiting policy
To configure rate limiting on a port, enter commands such as the following.
Brocade(config)#interface ethernet 24
Brocade(config-if-e1000-24)#rate input fixed 500
These commands configure a fixed rate limiting policy that allows port 24 to receive a maximum of
500 kbits per second. If the port receives additional bytes during a given one-second interval, the
port drops all inbound packets on the port until the next one-second interval starts.
Syntax: [no] rate-limit input fixed <average-rate>
For FastIron devices, the <average-rate> parameter specifies the maximum number of kilobits per
second (kbps) the port can receive. The minimum rate that can be configured is 64 kpbs.
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