在具有正常环回接口的 linux 机器上：
$ ifconfig lo
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:36621784 errors:0 dropped:0 overruns:0 frame:0
TX packets:36621784 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:6752024976 (6.2 GiB) TX bytes:6752024976 (6.2 GiB)
当我 ping 127.0.0.0/8 范围内的任何添加地址时，我会收到回复：
$ ping -c1 127.7.23.4
PING 127.7.23.4 (127.7.23.4) 56(84) bytes of data.
64 bytes from 127.7.23.4: icmp_seq=1 ttl=64 time=0.045 ms
--- 127.7.23.4 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, …