tl;dr: this post is about the free choice of routers to be used on home broadband connections in Germany. Since August 1st, a new law enables customers to receive credentials for the DSL connections as well as for VoIP services in order to use end devices (i.e. routers) of their choice. Since all of the following information are specific to one German local provider, NetCologne, the rest of the post is in German.
There is a command line tool called di which basically combines the information of df and mount.
While more and more ISPs and hosting providers start offering IPv6 subnets alongside with usual IPv4 addresses in dual-stack mode, there are still IPv4-only areas.