关闭ICMP协议(禁ping)
echo "1">/proc/sys/net/ipv4/icmp_echo_ignore_all
cat /proc/sys/net/ipv4/icmp_echo_ignore_all
打开ICMP协议(取消禁ping)
echo "0">/proc/sys/net/ipv4/icmp_echo_ignore_all
cat /proc/sys/net/ipv4/icmp_echo_ignore_all
原文：http://blog.51cto.com/wenjia111/2058950