除了 ping baidu.com

- http://www.gstatic.com/generate_204 288
- http://connectivitycheck.gstatic.com/generate_204 153
- http://captive.apple.com/ 146
- http://www.msftconnecttest.com/connecttest.txt 69
- http://edge.microsoft.com/captiveportal/generate_204 66
- http://detectportal.firefox.com/success.txt 41
- http://cp.cloudflare.com/generate_204 127
- http://www.qualcomm.cn/generate_204 62
- http://connect.rom.miui.com/generate_204 48
- http://connectivitycheck.platform.hicloud.com/generate_204 46
- http://wifi.vivo.com.cn/generate_204 65
- http://204.ustclug.org 84

(wget http://www.gstatic.com/generate_204 | % StatusCode ) -eq 204

来源 https://meta.appinn.net/t/topic/28925