Linux 中如何用iptables实现对外ping不回应,但对内ping给予回应?

禁用外网：
iptables -A INPUT -s 外网卡IP -p icmp --icmp-type echo-reply -j DROP

响应内网：

iptables -A icmp-acc -p icmp --icmp-type destination-unreachable -j ACCEPT
iptables -A icmp-acc -p icmp --icmp-type source-quench -j ACCEPT
iptables -A icmp-acc -p icmp --icmp-type time-exceeded -j ACCEPT
iptables -A icmp-acc -p icmp --icmp-type echo-request -j ACCEPT
iptables -A icmp-acc -p icmp --icmp-type echo-reply -j ACCEPT
iptables -A icmp-acc -j log-and-drop

请参考：
http://linux.chinaunix.net/doc/2004-10-05/15.shtml