mac系统不能使用127.0.0.2的解决方案

英语学得不好，国外这位大神的精彩解释不是特能看的懂。我模仿的试了一下。

解决方案：

1.打开mac终端

2.输入：sudo ifconfig lo0 alias 127.1.1.1 netmask 0xFFFFFFFF

3.浏览器测试。

（如果是127.0.0.2）应该就是：sudo ifconfig lo0 alias 127.0.0.2 netmask 0xFFFFFFFF

大神给予的解释：

FreeBSD (also OS X, and I believe NetBSD & OpenBSD) will respond to requests sent to configuredaddresses on the loopback interface, just as they would for addresses on any other interface -- If you want an answer you need to assign the address first:

mgraziano@monitor ~]$ ifconfig lo0
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
    options=3<RXCSUM,TXCSUM>
    inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
    inet6 ::1 prefixlen 128
    inet 127.0.0.1 netmask 0xff000000
    nd6 options=3<PERFORMNUD,ACCEPT_RTADV>

[mgraziano@monitor ~]$ ping 127.1.1.1
PING 127.1.1.1 (127.1.1.1): 56 data bytes
ping: sendto: Can't assign requested address
^C

[mgraziano@monitor ~]$ sudo ifconfig lo0 alias 127.1.1.1 netmask 0xFFFFFFFF

[mgraziano@monitor ~]$ ifconfig lo0
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
    options=3<RXCSUM,TXCSUM>
    inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
    inet6 ::1 prefixlen 128
    inet 127.0.0.1 netmask 0xff000000
    inet 127.1.1.1 netmask 0xffffffff
    nd6 options=3<PERFORMNUD,ACCEPT_RTADV>

[mgraziano@monitor ~]$ ping 127.1.1.1
PING 127.1.1.1 (127.1.1.1): 56 data bytes
64 bytes from 127.1.1.1: icmp_seq=0 ttl=64 time=0.020 ms
^C
On the logic behind this implementation, see RFC 3330:

127.0.0.0/8 - This block is assigned for use as the Internet host
loopback address. A datagram sent by a higher level protocol to an
address anywhere within this block should loop back inside the host.
This is ordinarily implemented using only 127.0.0.1/32 for loopback,
but no addresses within this block should ever appear on any network
anywhere [RFC1700, page 5].

来自国外：http://serverfault.com/questions/293874/why-cant-i-ping-an-address-on-the-loopback-device-under-freebsd