When you finish installing Ubuntu , you see that there is no network card when running "ifconfig" , or checking /etc/network/interfaces , but you see there is no info for your network card.

lspci -nn | grep -i net

The following command will show a list of ethernet card available in your Ubuntu box.

The output may look like this

09:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5761e Gigabit Ethernet PCIe (rev 10)

If you see the result, that means the network card has been recognized by your OS , then you just need to configure it

you can add these line to bring that interface up

auto eth0
iface eth0 inet static

Then run this :

ifup eth1

There is another tool to check the network card speed …

ethtool eth0