openwrt.network

Edit /etc/config/network. Under “WAN” section, set the configuration with:
config 'interface' 'wan'
        option 'ifname' 'eth0.2'
        option 'proto' 'pppoe'
        option 'username' 'your-own-username'
        option 'password' 'your-own-password'
        option 'defaultroute' '1'
        option 'peerdns' '1'
        
Force a re-dial
        ifdown wan
        ifup wan;        
        
http://wiki.openwrt.org/doc/uci/network#protocol.pppoe.ppp.over.ethernet

http://wiki.openwrt.org/doc/uci/network
http://wiki.openwrt.org/doc/networking/network.interfaces