ROUTERS
A router is a network communication device used to connect two or more logically and physically different networks. These devices are control center devices that compare the destination address information in the header of packets between networks with the routing table, make routing decisions and perform the transfer. The router, which works like a small computer, has its own memory and processor. It separates the IP address defined specifically for you and creates a separate IP for devices that establish a wireless or wired connection, allowing them to connect to the Internet. Each device must have an identity information in order to connect to the Internet. The router, which is responsible for security, ensures that this identity information is given. This identity is used to navigate the Internet.
Figure 1: Router Symbol
Routers can be used to connect a LAN to another LAN, a LAN to a WAN, or a LAN to the internet. If you were connecting to the internet with a device, you would not need a router, but everyone uses the internet through a computer, phone, tablet, television. In other words, almost every technological device in your home needs the internet. For this reason, you need a router. The router assigns an IP address to each device. In this way, a different signal is sent for each device. In short, the modem is the device that delivers the internet to you from the internet service provider. The router is the device that assigns different signals to the devices in your home.
Routers operate on the network layer of the OSI reference model because they work on the basis of IP addresses and have a built-in operating system known as IOS. This operating system can be programmed. It can perform routing by selecting the best of the available paths to reach a remote network.
A router in a network must look at the destination address of any packet and then determine which exit ports are the best options to deliver the packet to that address. The router makes this decision by looking at a routing table. The most important part of routing is to find the lowest cost path between any two nodes to which data will be transmitted.
A router connects devices like phones, tablets, and computers in your home directly to the internet, managing data flow as it's transmitted and received. It links your local area network (LAN) with a wide area network (WAN), that means behaves as bridge between your home network ant the broader internet. By examining various paths available on the internet, the router determines the fastest and most secure route for your data to travel, ensuring efficient transmission. Briefly the router functions as the gateway that connects your home to the internet.
On the other hand, a switch facilitates communication between multiple devices within the same local network. It receives data from these devices and directs it to the appropriate destination, effectively managing the internal data traffic in your home or office. While the router handles data exchange between different networks, the switch manages the flow of data between devices on the same local network, ensuring smooth and efficient communication.
Figure 2: Router / Switch
There are some routing protocols for routing.
Router Information Protocol (RIP): RIP is a distance-vector based routing protocol. Routers running this protocol send their entire routing tables to neighboring routers from all their ports at certain intervals (such as 30 seconds). Routers share information about computers or network devices connected to them with the routers they can reach. Information such as source IP address, gateway, distance, port number, timers are recorded in the routing table. In this way, a router can calculate which path it can take to reach the destination. The RIP protocol calculates by looking at the most suitable path hop count when choosing the best path. The best path information for each destination address is kept in the table. In practice, it is accepted that the hop count for RIP will be at most 15. Places farther than this value are considered unreachable. If the number of hops is 16 or more, this destination is considered unreachable.
Advantages
- RIP is simple and easy to use in small networks. Therefore, it is a widely used protocol.
Disadvantages
- It allows a maximum of 15 hops.
- Network traffic increases because it sends the routing table to neighboring routers that are directly connected continuously and at certain intervals.
- It causes problems in large networks.
OSPF (Open Shortest Path First) Protocol: It is a routing protocol developed to eliminate and correct some of the deficiencies in the RIP protocol. In this protocol, routers decide which path is the best by using the SPF [Shortest Path First] algorithms after reaching the information of all the paths between two points in the network. The OSPF algorithm can be likened to navigation devices that take us to any desired place in the shortest way. After choosing the shortest path to the destination, the connection is kept alive by sending small "hello" packets every 10 seconds.
Routers communicating with OSPF; know the information of neighbors, that is, the routers to which each leg is connected, in order to share the direction information to be traveled. OSPF shares information between devices and shares data such as table information with all routers.
Advantages
- OSPF protocol does not use metrics like distance vector protocols. There is no limitation on the number of steps.
- Route information is learned faster.
- Supports large networks.
Disadvantages
It is more difficult to configure and manage.
