Unable to get ethernet working on Colibri T20 module

I replaces rootfs with L4T as described here: http://developer.toradex.com/software-resources/arm-family/linux/images/using-the-nvidia-provided-l4t-rootfs
I successfully boot ubuntu on T20 board but it is not detecting ethernet.Please Help me.

I assume you are using the Toradex kernel? That would mean the kernel should still be able to detect it.

Does “ifconfig -a” show it?

Here is output of ifconfig -a : http://pastebin.com/C1xQtsNX

Here is console output: http://pastebin.com/qLvViMCU

The T30 has the Realtek ethernet adapter/driver, I’m assuming the same on the T20. From the paste output I see this for USB:

ASIX USB Ethernet Adapter:v4.4.0 02:38:38 Mar 20 2015
eth0: register 'asix' at usb-tegra-ehci.1-1, ASIX AX88772B USB 2.0 Ethernet, 00:14:2d:49:7d:cf

It looks like you have a USB ethernet NIC connected. Do you have an exact model?

FYI, I’ve had issues with installing multiple NICs (using a T30 with both the built-in Realtek and mPCIe Realtek in bridging mode for the purpose of some network simulation)…at least with the original Toradex rootfs, but no issue with Jetson using more modern L4T. Issues were related to u-boot doing initialization and no init other than module or driver loading…the first device set up always took on MAC address and other details from u-boot…adding a NIC caused the new NIC to work but disabled the built-in NIC (I had need for 3 NICs, one was USB).