internet issue on beagleboard-xm

I have loaded ubuntu 12.10 in sd card and booted it in beagleboard-xm rev c. After startup I entered ifconfig -a, I have found only lo and usb0 connections. I havent found eth0 there. I have connected lan cable from modem to ethernet port.But when i entered “sudo dhclient eth0”, it shows device cannot found. I need internet on my board for updating my packages.Is there anything to do to start internet connection via lan cable? Please help me to solve this issue.