title: Configure ROS_MASTER_URI & ROS_HOSTNAME
body: <p>I am not able to clearly understand the concept of ROS_MASTER_URI. Can someone kindly help me with the below?</p>
  <p>I have two systems. One robot which runs on ESP32 and connects via WiFi. I want this to be the slave device. On the other hand, I have a laptop which I want to be the master. I have followed a lot of tutorials and finally able to get it working, but the issue is if I change the network, what will happen?</p>
  <p>On the ESP32, I have below code:</p>
  <pre><code>IPAddress server(192, 168, 0, 110); // ip of ROS server -&gt; the laptop
  </code></pre>
  <p>On the laptop, there is still no ROS_MASTER_URI setup in bashrc file. I have manually checked the IP of the laptop and added that in ESP32. Now, how is this done? Every time the IP address of ROS changes in master, the same IP should be given on the slave device? This means, I need to reprogram it every time I go to a new location?</p>
  <p>Secondly, what are Host names and ROS_IP used for? Will they help if creating an alias which I can give to robot?</p>
  <p>In simple words, I do not want to open and reprogram the robot slave device every time I take my laptop to a new location. I should be able to change the IP on the laptop and somehow (magically :) work on the robot. Any help is extremely appreciated as I am struggling to get a solution from a week.</p>
  <p>-Praveen</p>