Ubuntu connectivity checking
This is a Gnome feature in NetworkManager that will check the network for you. This has been configured by Ubuntu to send a ping to connectivity-check.ubuntu.com every 300 seconds.
This comes from the package
network-manager-config-connectivity-ubuntu is installed by default and configures the NetworkManagers connectivity section. To see the config they have configured you can run
Making a request every 300 seconds really builds up. It soon become one of the most hit domains on my hole network. You can disable this by creating a new config file to set the
interval to 0.