router definition

Many devices and technologies are working together to enable a network. The primary device for networking is the router. The routers connect multiple networks. Communication between different networks is not possible without a router

. The main functions of the router are to decide the best path to the destination and send traffic to the next router along that path to the destination.

When a packet arrives on a router, the router uses a routing table to decide the best path for the destination network. The destination may be in the local area network or another country. The router is responsible for delivering this packet.

The effectiveness of communications between networks depends on the ability of routers to send packets in the most efficient way possible. The router does not have video and sound adapters like the computer. It has particular ports and network interface cards to interconnect devices to other networks. The essential parts of the router are the following:

• The central processing unit (CPU)
• Memory and storage (RAM, ROM, NVRAM, Flash, hard drive)
• Operating system (OS)

A router is a unique computer that uses a CPU to execute operating system instructions, such as system initialization, routing, and switching functions.

It also has a memory to store data temporarily and permanently. Cisco devices use the Cisco Internetwork Operating System (IOS) as the software. I already explained the router memory in one of my earlier articles:

Routers CPU, OS, and Memory

People don’t know whether various routers are present on their network or on the Internet. Users want to access web pages, read and send emails, and download music, videos, and software without knowing whether the server accessed is on their network or another network.

Only the networking professionals can understand the router’s responsibility for forwarding packets from network to network, from the source to the destination.

A router connects and communicates between multiple networks. It has multiple interfaces that each belong to a different IP network. When the router receives an IP packet on one of the interfaces, it determines the interface for forwarding the packet to the destination. The interface router forwarding the packet may be the destination or a network linked to another router used to reach the destination.

Each network typically requires a separate interface. Both local-area networks and wide-area networks interconnect through these interfaces. LANs contain devices such as PCs, printers, and servers. WANs connect networks over a large geographical area. For example, a WAN connection is commonly used to connect a LAN to the Internet. The primary functions of the router are the following:

• Select the best path to send packets
• Forward packets to their destination

The router selects the best path for forwarding data based on its routing table. After receiving a packet, the router examines the packet’s destination IP address and searches the best path in the routing table.

The routing table knows the interfaces to send packets for each known network. When a match is found in the routing table, the router sends the packet into the data link frame of the outgoing interface, and the packet is forwarded toward its destination.

The router has different types of interfaces, so it is possible for a router to receive a packet encapsulated in one kind of data link frame and to send the packet out of an interface using a different kind of data link frame. For example, a router receives a packet on an Ethernet interface. Still, the exit port is Point-to-Point Protocol (PPP), so the data is encapsulated in another data link frame type.

A router can connect to different data link technologies, including Ethernet, PPP, Frame Relay, DSL, cable, and wireless (802.11, Bluetooth). Routers use both static routes and dynamic routing protocols to learn about remote networks and maintain routing tables.

functions of a router in a network

Function	Description
Packet Forwarding	Routers forward data packets between different networks, determining the best path based on routing tables.
Network Layer Routing	Routers connect multiple networks, enabling communication between devices on different networks.
Interconnect Networks	Routers support VPN connections, allowing remote users to access the network over the internet securely.
Traffic Control	Routers manage network traffic by prioritizing packets, implementing Quality of Service (QoS), and controlling bandwidth usage.
Security	Routers provide security features such as access control lists (ACLs), firewalls, and virtual private network (VPN) support to protect networks from unauthorized access and attacks.
NAT (Network Address Translation)	Routers perform NAT to translate private IP addresses to public IP addresses, allowing devices on a private network to access the internet.
DHCP (Dynamic Host Configuration Protocol)	Routers can act as DHCP servers, dynamically assigning IP addresses and other network configuration parameters to devices on a network.
VPN (Virtual Private Network)	Routers support VPN connections, allowing remote users to securely access the network over the internet.
Load Balancing	Routers distribute network traffic across multiple links or paths to optimize performance and prevent congestion.
Redundancy	Routers support redundancy protocols such as HSRP (Hot Standby Router Protocol) and VRRP (Virtual Router Redundancy Protocol) to ensure high availability and fault tolerance.