这个配置比起原来的有固定ip地址的配置要难很多，要考虑到方方面面的东西，在这里，大家可以少走弯路了：
vpdn enable
no vpdn logging
!
vpdn-group pppoe
request-dialin
protocol pppoe
!
interface Ethernet0
no shut
ip address <ip address> <subnet mask>
ip adjust-mss 1452
ip nat inside
no ip directed-broadcast
!
interface ATM0
no shut
no ip address
no ip directed-broadcast
no atm ilmi-keepalive
bundle-enable
!
interface ATM0.1 point-to-point
no ip directed-broadcast
pvc <vpi/vci>
pppoe-client dial-pool-number 1
!
!
interface Dialer1
ip address negotiated
mtu 1492
ip nat outside
encapsulation ppp
dialer pool 1
ppp chap hostname <username>
ppp chap password <password>
ppp pap sent-username <username> password <password>
!
ip nat inside source list 1 interface Dialer1 overload
!
ip classless
ip route 0.0.0.0 0.0.0.0 dialer1
access-list 1 permit <ip address of ethernet0> 0.0.255.255