ROS Machine Communication between 4G/LTE USB dongle & static assigned Cable/DSL IP address

edit

I have to machine. One is Raspberry Pi with 4G/LTE USB dongle on it. It have IP address like 192.168.8.100. Another is PC, with static assigned Cable/DSL IP address like 140.113.xxx.xxx.

I type ifconfig to get the IP address I mention before. And I follow the Section 5.4 "Network configuration" in the links link text to setup.

I already try two machine with both "static assigned Cable/DSL IP address" type, and it communicate successfully. But when I change the Pi's internet to the 4G USB dongle, and run roslaunch ,it shows the following error:

cannot resolve host address for machine [localhost]

It wonder that how to deal with the situation with communication between "machine with 4G USB dongle" & "machine with static assigned Cable/DSL IP address", because I still can't find the setting method to make it work.

Any help will be appreciated,tks!