执行以下命令禁用 ping 回复后：
# sysctl net.ipv4.icmp_echo_ignore_all=1
# sysctl -p
我从 ping localhost 与 127.0.0.1 获得不同的结果
# ping -c 3 localhost
PING localhost(localhost (::1)) 56 data bytes
64 bytes from localhost (::1): icmp_seq=1 ttl=64 time=0.029 ms
64 bytes from localhost (::1): icmp_seq=2 ttl=64 time=0.035 ms
64 bytes from localhost (::1): icmp_seq=3 ttl=64 time=0.101 ms
--- localhost ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2042ms
rtt min/avg/max/mdev = 0.047/0.072/0.101/0.022 ms
Ping 127.0.0.1 失败：
ping -c 3 127.0.0.1 …