这个 DNS 问题好奇怪， ping， nslookup 都不好使了，但是网站访问正常。

> sudo discoveryutil mdnsflushcache

Password:
> sudo discoveryutil udnsflushcaches

>
> clear
> ping www.baidu.com
PING www.baidu.com (127.128.0.58): 56 data bytes
Request timeout for icmp_seq 0
^Z
[5] + 875 suspended ping www.baidu.com
> nslookup www.baidu.com
Server: 223.5.5.5
Address: 223.5.5.5#53

Non-authoritative answer:
Name: www.baidu.com
Address: 127.128.0.58

> nslookup www.sina.com
Server: 223.5.5.5
Address: 223.5.5.5#53

Non-authoritative answer:
Name: www.sina.com
Address: 127.128.0.250

> nslookup www.weibo.com
Server: 223.5.5.5
Address: 223.5.5.5#53

Non-authoritative answer:
Name: www.weibo.com
Address: 127.128.0.251

> nslookup www.qq.com
Server: 223.5.5.5
Address: 223.5.5.5#53

Non-authoritative answer:
Name: www.qq.com
Address: 127.128.0.252

> nslookup fuckyou.com
Server: 223.5.5.5
Address: 223.5.5.5#53

Non-authoritative answer:
Name: fuckyou.com
Address: 127.128.0.253

> nslookup xljklsjfljlwejrojsdljfkljwejlfsd.com
Server: 223.5.5.5
Address: 223.5.5.5#53

Non-authoritative answer:
Name: xljklsjfljlwejrojsdljfkljwejlfsd.com
Address: 127.128.0.254

>

每次解析到的IP都是+1，都是内网地址。
比如这次解析到的IP是：127.128.0.2
下次随便一个域名解析到的IP就是：127.128.0.3

我用的阿里DNS呀，换百度的DNS结果也是一样的。

奇怪的是浏览器访问各个网站都是很正常的。命令行下用TCP模式也能正常。