KB.15.15

Figure 84 ICMP rate-limiting

NOTE: When using kbps-mode ICMP rate-limiting, the rate-limiting operates on only the IP payload

part of the ICMP packet (as required by metering RFC 2698.) This means that effective metering

is at a rate greater than the configured rate, with the disparity increasing as the packet size

decreases (the packet to payload ratio is higher.)

Also, in kbps mode, metering accuracy is limited at low values, for example, less than 45 Kbps.

This is to allow metering to function well at higher media speeds such as 10 Gbps.

Using both ICMP rate-limiting and all-traffic rate-limiting on the same interface

ICMP and all-traffic rate-limiting can be configured on the same interface. All-traffic rate-limiting

applies to all inbound or outbound traffic (including ICMP traffic), while ICMP rate-limiting applies

only to inbound ICMP traffic.

NOTE: If the all-traffic load on an interface meets or exceeds the currently configured all-traffic

inbound rate-limit while the ICMP traffic rate-limit on the same interface has not been reached, all

excess traffic is dropped, including any inbound ICMP traffic above the all-traffic limit (regardless

of whether the ICMP rate-limit has been reached.)

Example

Suppose:

• The all-traffic inbound rate-limit on port "X" is configured at 55% of the port's bandwidth.

• The ICMP traffic rate-limit on port "X" is configured at 2% of the port's bandwidth.

If at a given moment:

• Inbound ICMP traffic on port "X" is using 1% of the port's bandwidth, and

• Inbound traffic of all types on port "X" demands 61% of the ports's bandwidth,

all inbound traffic above 55% of the port's bandwidth, including any additional ICMP traffic, is

dropped as long as all inbound traffic combined on the port demands 55% or more of the port's

bandwidth.

Operating notes for ICMP rate-limiting

ICMP rate-limiting operates on an interface (per-port) basis to allow, on average, the highest

expected amount of legitimate, inbound ICMP traffic.

Interface support ICMP rate-limiting is available on all types of ports (other

than trunk ports or mesh ports), and at all port speeds

configurable for the switch.

188 Port Traffic Controls