openwrt使用pptp客户端如何让lan口的用户都走vpn通道？

我想让openwrt的路由器帮我pptp拨号，然后所有路由器的用户都走vpn通道，按照官方wiki设置后不能正常工作（无法访问任何外网）。

已经添加了一个vpn接口，ifconfig后主要的Interface：
br-lan Link encap:Ethernet HWaddr xx:xx:xx:xx:xx:xx
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::21e:40ff:fe30:84d7/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:6248 errors:0 dropped:0 overruns:0 frame:0
TX packets:1701 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:438624 (428.3 KiB) TX bytes:480666 (469.4 KiB)

pptp-vpn Link encap:Point-to-Point Protocol
inet addr:192.168.0.200 P-t-P:192.168.0.1 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1452 Metric:1
RX packets:51 errors:0 dropped:0 overruns:0 frame:0
TX packets:53 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:1710 (1.6 KiB) TX bytes:4905 (4.7 KiB)

eth0 Link encap:Ethernet HWaddr xx:xx:xx:xx:xx:xx
inet addr:x.x.x.18 Bcast:49.209.5.255 Mask:255.255.254.0
inet6 addr: fe80::21e:40ff:fe30:84d6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:68121 errors:0 dropped:0 overruns:0 frame:0
TX packets:70547 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:7576449 (7.2 MiB) TX bytes:4316878 (4.1 MiB)
Interrupt:16

路由表：
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.0.1 * 255.255.255.255 UH 0 0 0 pptp-vpn
192.168.1.0 * 255.255.255.0 U 0 0 0 br-lan
x.x.x.0 * 255.255.254.0 U 0 0 0 eth0
default x.x.x.1 0.0.0.0 UG 0 0 0 eth0

(出于隐私上面eth0即wan口的ip前三段用x.x.x表示了）

按照上面是没有走pptp通道，现在怎样让所有lan口的客户机走pptp通道，当然连接路由器要能连接上。