Windows XP windows size default is too small

The default vaule is 64K, it will impact the throughput test.

You need to modify the value if you want to get good throughput test result.

pptpd debug

start pptpd in debug mode:
pptpd -d

read the debug log in syslog:
cat /var/log/syslog

[problem]
connection failed, and debug message show "mppe required but peer refused" :
you need to force the client to use mppe encryption or close the mppe encryption option on server.

pptp client can't get dns server ip:
set the ms-dns option on the server side, let the client can get ip.