A router is a switching device for networks, which is able to route network packets, based on their addresses, to other networks or devices. Among other things, they are used for Internet access, for coupling networks or for connecting branch offices to a central office via VPN (Virtual Private Network). Depending on the type they communicate using the various access protocols, such as Ethernet, ATM or DSL. In the OSI layer model, the switching of data packets through the router is based on the address on the network layer (layer 3). In addition to routers that use Internet protocol (IP), there are multi-protocol routers, which also handle other network protocols.