Linux 搭建PPTP Server连接超过100个后，就再无法拨号成功了。
查看log 发现有以下信息：
# logread |grep -v "GRE"
Nov 20 11:17:13 pptpd[21132]: CTRL: Received PPTP Control Message (type: 5)
Nov 20 11:17:13 pptpd[21132]: CTRL: Made a ECHO RPLY packet
Nov 20 11:17:13 pptpd[21132]: CTRL: I wrote 20 bytes to the client.
Nov 20 11:17:13 pptpd[21132]: CTRL: Sent packet to client
#man pptpd.conf
connections n
limits the number of client connections that may be accepted.
If pptpd is allocating IP addresses (e.g. delegate is not used)
then the number of connections is also limited by the remoteip
option. The default is 100.
PPTP Server 最大连接数，是connections和地址池数量一起控制的，connections默认是100，导致无法连接更多。
如果希望最大连接1000条，可以在pptpd.conf中添加一行配置(地址池要有1000个地址)：
connections 1000
