9

I have mistakenly thought that the limit module is per source ip, but it appears to be based on all requests:

  577 36987 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 limit: avg 3/sec burst 5 
   46  3478 LOG        icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 LOG flags 0 level 4 prefix `INET-PING-DROP:' 
   46  3478 DROP       icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 
    ...
    0     0 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 limit: avg 3/sec burst 5 
    0     0 LOG        icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 LOG flags 0 level 4 prefix `WEB-PING-DROP:' 
    0     0 DROP       icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 

How can I rate limit icmp with iptables / netfilter based on the source IP address?

5

If you were still wondering for a hint:

iptables -I INPUT -p icmp -m hashlimit --hashlimit-name icmp --hashlimit-mode srcip --hashlimit 3/second --hashlimit-burst 5 -j ACCEPT

Assuming the last rule in INPUT is drop or the default policy is DROP. Each ip is limited to 3 pings a second (burst of 5). Not all incoming IPs total, as you found with -m limit.

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