Why is my CentOS box rejecting some (but not all) ICMP ping requests from the same remote host?

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http://serverfault.com – CentOS 4.x I've got several old CentOS 4.x systems and have configured iptables to allow ICMP traffic. Originally, I had an iptables rule that looked like: -A RH-Firewall-1-INPUT -p icmp --icmp-type echo-request -m limit --limit 1/s -j ACCEPT That seemed to work fine for awhile but one of our monitoring solutions has a requirement to ping more often than once a second (long story but in short, it's a requirement). To accommodate this, I changed the rule to: -A RH-Firewall-1-INPUT -p icmp --icmp-type echo-request -j ACCEPT The strange part is that I have this same rule on multiple (HowTos)