Router (CIE IGCSE Computer Science)

• A router is an important piece of network hardware. It connects one network to another network
  • This means it can be used to connect a local area network (LAN ) to the internet, which is a wide area network(WAN )

• An important role of the router is to analyse data packet  and direct them on to their destination
  
  

 

A diagram showing multiple networks connected by routers, represented by the blue circular objects

• A router being used to connect a LAN to a WAN will have a public IP address , which has been assigned to it by an Internet Service Provider
• It is this public IP address which other routers use to identify and direct packets to the network
• An important role of the router is to analyse data packets and direct them on to their destination
  • The IP address of both the sender and intended recipient is stored in the header of the data packet
    • The header contains information about the packet
    • The payload is the actual data being sent
• If the data packet is coming into the LAN, the router will send the data packet to the specific device, within its LAN, that the packet is meant for
• If the packet is being sent from a device within the LAN, it will read the header of the packet to determine the intended destination IP address
  • It will then forward the packet on to the destination
    • It might have to travel through several routers before it gets to its destination
    • Each pass from router to router is called a hop
• The network access device or ‘home hub’ used in your home network will have a router built into it

A summary of the steps a router takes when it receives a data packet

Step	Description
1	a router receives incoming data packets from one network and analyses the packet header to determine the destination IP address
2	It then looks up the IP address in a routing table (routing table of known networks) to determine the next network where the packet should be sent
3	The router then forwards the packet to the appropriate network or device

• This process is repeated by every router the data packet passes through, until it reaches its destination
• In addition to routing data between networks, routers can also perform other functions such as…
  • assigning IP addresses to devices within the LAN
  • filtering incoming traffic based on certain criteria, such as IP address, port number, or protocol type