求助：路由交換-關於×××虛擬私有網二層隧道協議的問題

今天在作一個×××時有個關於虛擬私有網二層隧道協議的問題，搭建一個撥號鏈接網絡。我是利用一個路由模擬器作的。

實驗以下：

拓撲圖：

 

這些都是路由器，我是利用路由R四、R五、R6作的。

具體配置以下：

客戶機:

IP：192.168.10.10 GW：192.168.10.1

作一個撥號鏈接，指向主機IP：192.168.30.2
路由器配置以下：

R4:
f0/0:192.168.10.1
s1/1:192.168.20.1
R5:
s1/0:192.168.20.2
s1/1:192.168.30.1
R6:
s1/0:192.168.30.2
F2/0:192.168.50.1

R4:

ena
conf t
hostname R4
int f0/0
ip add 192.168.10.1 255.255.255.0
ip nat inside
no shut
exit
int s1/1
ip add 192.168.20.1 255.255.255.0
ip nat outside
no shut
exit
access-list 1 permit 192.168.10.0 0.0.0.255
ip nat inside source list 1 int s1/1 overload
ip route 0.0.0.0 0.0.0.0 s1/1
end

R5:

ena
conf t
hostname R5
int s1/0
ip add 192.168.20.2 255.255.255.0
no shut
exit
int s1/1
ip add 192.168.30.1 255.255.255.0
no shut
end

R6:

ena
conf t
hostname R6
username chensong password 123
ip local pool jintian 192.168.50.10 192.168.50.100
vpdn enable
vpdn-group pptp
accept-dialin
protocol pptp
virtual-template 1
exit
int virtual-template 1
ip unnumbered s1/0
no shut
enca ppp
ppp authen ms-chap
peer default ip add pool jintian
exit
int s1/0
ip add 192.168.30.2 255.255.255.0
ip nat outside
no shut
exit
int f2/0
ip add 192.168.50.1 255.255.255.0
ip nat inside
no shut
exit
access-list 1 permit 192.168.50.0 0.0.0.255
ip nat inside source list 1 int s1/0 overload
ip route 0.0.0.0 0.0.0.0 s1/0
end
 

配置如上，可是問題出在最後我撥號鏈接的時候，提示：遠程主機無反應……

但願各位大大給我說說，個人問題出如今哪裏？