What is a router?

A router is a network device that connects different computer networks by routing packets from one network to the other. This device is usually connected to two or more different networks. When a data packet comes to a router port, the router reads the address information in the packet to determine out which port the packet will be sent. For example, a router provides you with the internet access by connecting your LAN with the Internet.

A router is considered a Layer 3 device of the OSI model because its primary forwarding decision is based on the information of the OSI Layer 3 (the destination IP address). If two hosts from different networks want to communicate with each other, they will need a router between them. Consider the following example:

how routers work

We have a network of three computers. Note that each computer is on a different network. Host A wants to communicate with Host B and sends a packet with Host B’s IP address ( to the default gateway (the router). The router receives the packet, compares the packet’s destination IP address to the entries in its routing table and finds a match. It then sends the packet out the interface associated with that network. Only Host B will receive the packet. In fact, Host C will not even be aware that the communication took place.


Each port on a router is in a separate collision and broadcast domain and can run in the full duplex mode.
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