What is ICMP? ICMP stands for "Internet Control Message Protocol" All machines have now been set up to filter and deny ICMP packets such as ICMP ECHO (Ping) on each of the machines main IP's. The deny is setup on only the main IP, filtering is effective on all IP's - I will not cover filtering as it is out of the scope of this thread.
What does this mean for my sites on the server? This means that if you traceroute or ping to the servers main IP address, you will be returned with a "Timed out message" - This is perfectly normal and is what should be happening. It is still possible to carry out traces and pings to the unique IP you have been assigned with however. Web monitoring software that monitors http/https connections to the server is unaffected and will still work. Pings to the server will however not return a response. Why? ICMP packet abuse is a problem. There are still many low level denial of service attacks happening due to icmp echo- reply abuse - The requests fill up the data pipe to the server, slowing the connection down, wasting bandwidth and in some cases will actually crash the server, rendering it unavailable. What is a DOS attack? A denial of service attack (DOS) is any action taken by someone with the intention to cause a service to become unavailable or unusable. Blocking ICMP packets at the server, will not stop many DOS or DDOS attacks, as they need to be controlled and filtered at router level - However there are many types of more frequent attack that blocking ICMP requests at the server will control. I hope that this will alleviate any concerns that you may have regarding the output from your pings and traces that are returning strange results.
