user a pass 0 a
int aux 0
modem
asy mode ded
ip add 172.40.125.1 255.255.255.0
ppp auth pap
shut
no shut
int e 0
ip add 172.30.125.1 55.255.255.0
pc 的ip需要设置为172.40.125.**

　　内容配置不完整,加上下面的配置

dialer-list 1 prot ip perm
ip local pool 1 172.40.125.2 172.40.125.3
int aux0
dialer in-band
dialer-group 1
peer default ip addr pool 1
baudrate 38400