What are these messages about ``icmp-response bandwidth limit 300/200 pps'' in my log files?

This is the kernel telling you that some activity is provoking it to send more ICMP or TCP reset (RST) responses than it thinks it should. ICMP responses are often generated as a result of attempted connections to unused UDP ports. TCP resets are generated as a result of attempted connections to unopened TCP ports. Among others, these are the kinds of activities which may cause these messages:

The first number in the message tells you how many packets the kernel would have sent if the limit was not in place, and the second number tells you the limit. You can control the limit using the net.inet.icmp.icmplim sysctl variable like this, where 300 is the limit in packets per second:

    # sysctl -w net.inet.icmp.icmplim=300

If you do not want to see messages about this in your log files, but you still want the kernel to do response limiting, you can use the net.inet.icmp.icmplim_output sysctl variable to disable the output like this:

    # sysctl -w net.inet.icmp.icmplim_output=0

Finally, if you want to disable response limiting, you can set the net.inet.icmp.icmplim sysctl variable (see above for an example) to 0. Disabling response limiting is discouraged for the reasons listed above.



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