My server is constantly attacked by SMS bombing, iis log every day more than 100 MB
Iis specific log below

POST/index. PHP/passport - send_vcode_sms. HTML - 80-221.225.205.206 Mozilla/5.0 + (+ Windows NT + 6.3; + Win64; 537.36 + + x64) + AppleWebKit/(KHTML, + + Gecko like) + Chrome/Safari 39.0.2171.99 +/537.36 200 0 0, 236
POST/index. PHP/passport - send_vcode_sms. HTML - 80-222.222.156.181 Mozilla/5.0 + (+ Windows NT + 6.3; + Win64; 537.36 + + x64) + AppleWebKit/(KHTML, + + Gecko like) + Chrome/Safari 39.0.2171.99 +/537.36 200 0 0, 237
POST/index. PHP/passport - send_vcode_sms. HTML - 80-123.232.138.80 Mozilla/5.0 + (+ Windows NT + 6.3; + Win64; 537.36 + + x64) + AppleWebKit/(KHTML, + + Gecko like) + Chrome/Safari 39.0.2171.99 +/537.36 200 0 0, 307

Attack about 50 times per second, could you tell me how to defense, or let the log does not record these information?

server environment
Run the application: ecshop
Windows Server 2008 R2 enterprise x64
Iis 7
Mysql 5.5
PHP 5.3.0 - NTS - Win32 - VC9 - x86