OpenWrt/ImmortalWrt 配置NJU BRAS校外拨入

OpenWrt/ImmortalWrt 配置南京大学的BRAS校外拨入（L2TP），添加策略路由仅让访问校内IP走VPN。

用 opkg 安装 xl2tpd 及其依赖包，在 /etc/config/network 中添加如下配置，其中将***替换为统一认证的用户名密码。完成后在网络-接口中可见名为nju的接口，开机会自动链接。

config interface 'nju'
	option proto 'l2tp'
	option server '202.119.36.101'
	option username '***'
	option password '***'
	option ipv6 '0'
	option mtu '1452'
	option defaultroute '0'
	option delegate '0'
	option ip4table 'main'

config route
	option interface 'nju'
	option target '114.212.0.0/16'
	option mtu '1452'

config route
	option interface 'nju'
	option target '180.209.0.0/20'
	option mtu '1452'

config route
	option interface 'nju'
	option target '202.119.32.0/19'
	option mtu '1452'

config route
	option interface 'nju'
	option target '202.127.247.0/24'
	option mtu '1452'

config route
	option interface 'nju'
	option target '202.38.126.160/28'
	option mtu '1452'

config route
	option interface 'nju'
	option target '202.38.2.0/23'
	option mtu '1452'

config route
	option interface 'nju'
	option target '210.28.128.0/20'
	option mtu '1452'

config route
	option interface 'nju'
	option target '210.29.240.0/20'
	option mtu '1452'

config route
	option interface 'nju'
	option target '219.219.112.0/20'
	option mtu '1452'

config route
	option interface 'nju'
	option target '58.192.32.0/20'
	option mtu '1452'

config route
	option interface 'nju'
	option target '58.192.48.0/21'
	option mtu '1452'

config route
	option interface 'nju'
	option target '58.193.224.0/19'
	option mtu '1452'

config route
	option interface 'nju'
	option target '58.195.80.0/20'
	option mtu '1452'