配置的示例在聚合器的显示：
interface GigabitEthernet0/0/1
ip address 192.168.1.1 255.255.255.0
negotiation auto
end interface Loopback100
ip address 172.16.1.1 255.255.255.255
end vpdn enable
vpdn-group 1
! Default L2TP VPDN group
accept-dialin
protocol l2tp
virtual-template 1
no l2tp tunnel authentication interface Virtual-Template1
ip unnumbered Loopback100
peer default ip address pool test
ppp authentication chap callout
ppp ipcp dns 4.2.2.1 4.2.2.2
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debug ppp negotiation 可以debug 查看注册信息
