Can't ssh by name with more than 3 robots

edit

I am using a main computer to launch the ros nodes in 4 robots. These robots have odroids. I can ssh into the robots by name:

ssh odroid@odroid-machine1.local
ssh odroid@odroid-machine2.local
ssh odroid@odroid-machine3.local
ssh odroid@odroid-machine4.local

I can ssh by name to all the robots except 1 odroid@odroid-machine4.local. To that one I need to ssh by ip address but I need to ssh by name to launch the nodes on it.

The network is done with a router, and something funny is happening. If I do not connect the router to internet I cannot ssh odroid-machine4.local by name, only by ip address. If a connect the router to internet everything is fine. The thing is that for some of my experiments I need to move to a place where I do not have internet access.

I think I might have some configuration problems but I do not know how to debug them.

Today I reinstalled Ubuntu from zero on odroid-machine4.local. Then I reinstalled all the software and configured the network as I always do for all the robots. I was able to ssh odroid-machine4.local by name. Then I connected all the robots to the network and again odroid-machine4.local was not recognized by name. It was until I connected the router to internet that I was able to ssh by name.

I even tried with a different router and I have the same problem.

I think I need to configure something but I don't know what.