1. Changes to do in BSP LSDK.
For RAMDISK-based rootfs types: See LSDK User Guide Section 4.3.13 for steps to unpack, modify and rebuild rootfs image and the manpage for /etc/network/interfaces for necessary changes.
For SD/eMMC rootfs: none. All necessary changes can be done in runtime.
2. In runtime Linux environment.
Familiarize yourself with manpages for ifconfig and /etc/network/interfaces.
Hope this helps,
Platon