On a machine called ubuntu1, this is the iptables command:sudo iptables -A INPUT -p icmp -j DROPon the other computer (xp1) I can not ping the ubuntu1.So this is OK.But On ubuntu1 can ping xp1. and I think this is not OK. I do not have problem with ping request but I have problem with ping replay from xp1. Why does that command not drop the replay of ping which is an ICMP packet?UPDATE:I did a mistake . I did not see the replay on terminal!!! I just see the replay on wireshark.!!! 
iptables INPUT command
iptables;firewall
The command which you are entering is just for blocking incoming ICMP connection if you want to block outgoing ICMP connection you have to choose output chain i.e sudo iptables -A OUTPUT -p icmp -j DROP