Static IP address
From Tekkotsu Wiki
You can force your robot to use a static IP address rather than obtain one dynamically from a DHCP server. Dynamic IP addresses are better because they allow the robot to run on whatever network it finds, but in circumstances where a DHCP server is not available or is not cooperating (e.g., you take your robot to another location and the local network refuses to assign you an IP address, or you're trying to control the robot from someone's laptop and they are unable to set up a DHCP server), use a static address.
We assume the robot is running Ubuntu Linux, or a variant such as Easy Peasy.
Edit the file /etc/network/interfaces:
Modify the entry for eth0, or add a new entry if there is none, as follows:
auto eth0 iface eth0 inet static address 192.168.1.123 the IP address you've chosen for the robot netmask 255.255.255.0
To put this change into effect, do:
sudo ifdown eth0 if this fails, ignore it sudo ifup eth0
If you want to go back to using a dynamic IP address, replace the above lines in /etc/network/interfaces with the following:
auto eth0 iface eth0 inet dhcp