Network Routing

In today’s world, we are very often physically in different geographical locations, but actually speaking we are always in touch with one another. In our professional life, we engage in Work from home culture or video calls with our counterparts in different locations or be it our personal life with all the social media platforms, we are always connected. According to a survey, in 2012 there were 8.7 billion number of connected devices worldwide and now in 2020 we have around 50 billion connected devices and its always growing. All these are only possible using one thing i.e. networking.

First, we should all know what network is. A computer network is a digital telecommunications platform for sharing resources between nodes, which are computing devices that use a common telecommunications technology. Data transmission between nodes is supported over data links consisting of physical cable media, such as twisted pair or fibre-optic cable or by wireless methods, such as Wi-Fi, microwave transmission, or free-space optical communication. There are two types of network: wired and wireless.

• Wired network means network using the physical medium like cables. For example: LAN (Local Area Network) connection using RJ-45 cables.
• Wireless network means network using medium, made of electromagnetic waves (i.e. EM Waves) or infrared waves. Example: Wi-Fi, Bluetooth.

Now, in networking we need to understand that how data gets transferred from source to destination. One of the main components of the data transfer process is network routing.

When a device has multiple paths to reach a destination, it always selects one path by preferring it over others. This selection process is termed as Routing. Routing is done by special network devices called routers. A router is always configured with some default route. A default route tells the router where to forward a packet (packet is a unit of data used to transmit info in Network Layer) if there is no route found for specific destination.

When a packet arrives at a Router, it examines destination IP address of a received packet and make routing decisions accordingly. Routers use Routing Tables to determine out which interface the packet will be sent. A routing table lists all networks for which routes are known. Each router’s routing table is unique and stored in the RAM of the device.

A routing table is a set of rules, often viewed in table format, that is used to determine where data packets traveling over an Internet Protocol (IP) network will be directed. All IP-enabled devices, including routers and switches, use routing tables. See below a Routing Table:

Destination     Subnet Mask          Interface

128.75.43.0     255.255.255.0         Eth0

128.75.43.0     255.255.255.128     Eth1

192.12.17.5     255.255.255.255     Eth3

default                                             Eth2

The entry corresponding to the default gateway configuration is a network destination of 0.0.0.0 with a network mask (netmask) of 0.0.0.0. The Subnet Mask of default route is always 255.255.255.255.A routing table contains the information necessary to forward a packet along the best path toward its destination. Each packet contains information about its origin and destination. Routing Table provides the device with instructions for sending the packet to the next hop on its route across the network.Each entry in the routing table consists of the following entries:

1.   Network ID: The network ID or destination corresponding to the route.

2.   Subnet Mask: The mask that is used to match a destination IP address to the network ID.

3.   Next Hop: The IP address to which the packet is forwarded.

4.   Outgoing Interface: Outgoing interface the packet should go out to reach the destination network.

5.   Metric: A common use of the metric is to indicate the minimum number of hops (routers crossed) to the network ID.

When a router receives a packet, it examines the destination IP address, and looks up into its Routing Table to figure out which interface packet will be sent out.

These Routing tables can be maintained manually or dynamically. In dynamic routing, devices build and maintain their routing tables automatically by using routing protocols to exchange information about the surrounding network topology. Dynamic routing tables allow devices to “listen” to the network and respond to occurrences like device failures and network congestion. Tables for static network devices do not change unless a network administrator manually changes them.

Different types of routing are :

• Unicast routing: Most of the traffic on the internet and intranets known as unicast data or unicast traffic is sent with specified destination. Routing unicast data over the internet is called unicast routing. It is the simplest form of routing because the destination is already known. Hence the router just have to look up the routing table and forward the packet to next hop.
• Broadcast routing: By default, the broadcast packets are not routed and forwarded by the routers on any network. Routers create broadcast domains. But it can be configured to forward broadcasts in some special cases. A broadcast message is destined to all network devices. Broadcast routing can be done in two ways (algorithm):

· A router creates a data packet and then sends it to each host one by one. In this case, the router creates multiple copies of single data packet with different destination addresses. All packets are sent as unicast but because they are sent to all, it simulates as if router is broadcasting. This method consumes lots of bandwidth and router must know the destination address of each node.

· Secondly, when router receives a packet that is to be broadcasted, it simply floods those packets out of all interfaces. All routers are configured in the same way. This method is easy on router’s CPU but may cause the problem of duplicate packets received from peer routers. · Reverse path forwarding is a technique, in which router knows in advance about its predecessor from where it should receive broadcast. This technique is used to detect and discard duplicates.

• Multicast Routing: Multicast routing is special case of broadcast routing with significance difference and challenges. In broadcast routing, packets are sent to all nodes even if they do not want it. But in Multicast routing, the data is sent to only nodes which wants to receive the packets. The router must know that there are nodes, which wish to receive multicast packets (or stream) then only it should forward. Multicast routing also uses reverse path Forwarding technique, to detect and discard duplicates and loops.
• Anycast Routing: Anycast packet forwarding is a mechanism where multiple hosts can have same logical address. When a packet destined to this logical address is received, it is sent to the host which is nearest in routing topology. Anycast routing is done with help of DNS server. Whenever an Anycast packet is received it is enquired with DNS to where to send it. DNS provides the IP address which is the nearest IP configured on it.

The advantages of Routers are:

1. Routers can connect different network architectures.
2. Routers can choose best path across the network using the dynamic routing techniques.
3. Routers reduce network traffic.

The shortcomings of Routers are:

1. Routers work only with routable network protocols, not all protocols are routable
2. Routers are more expensive than bridges or repeaters.

So, today in the world of digitalization, Networking is a critical component. It is one of the main media of Global business. With the emerging Global Economy and their related data, there is a lot of scope of increasing the Networking manifold in terms of video, audio and data transmission. In the future generations, the data to be transmitted will be much more than today, so we all should understand about the network and strive for the enhancement of the network.

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