What are the basic routing concepts? Packet forwarding, Router lookup process and process switching:

Certification: Cisco CCIE Routing and Switching - Cisco Certified Internetwork Expert Routing and Switching

Routing is a simple process in computing used to find the best path in the network and is usually carried out in different kind of networks including the transportation networks, data networks such as the internet and also in the telephone networks. The most common place where the routing concept is applied is in the packet switching networks where routing uses the available intermediate nodes to direct any packet forwarding whereby the intermediate nodes that are used as medium are typically hard devices such as  the bridges, gateways, firewalls, switches and routers. The routing table is usually the point where the routing process usually directs the correct forwarding. It uses one assumption that the network addresses are usually structured and as a result there are different kinds of delivery semantics that are used to determine the structure of a particular routing system.

The structures of the routing system:

There are basically five different structures that are used to describe the manner in which the routing process is carried out:

  • Unicast

Which is common when it comes to the routing process, usually delivers messages to specifically one node assigned to it.

  • Anycast

This routing scheme is designed in such a way that its function is to deliver messages to any of the nodes that appear to be close to it and the node should be outside a group of nodes.

  • Multicast

In this case there is delivery of messages to a group of nodes that are interested in receiving that particular message.

  • Broadcast

All the nodes within a certain broadcasting domain receive the message that has been sent.

  • Geocast

This is a special type since it has the ability to transmit messages to a whole geographic area.

Routing can be further be divided into two groups; the non adaptive routing commonly known as the static routing system that  is usually applied in small networks that have been configured manually using the routing tables. The second type is the adaptive routing system that is widely used in the internet and it is also known as dynamic routing where the routing tables are usually constructed automatically and found in most public networks whose routing protocols purely based on the available information. The advantage of this type of routing is that chances of network failure are very less and it can also be used to cover a wide area since it is easy to access.

In the routing process there are certain basic concepts that are of importance and they include:  packet forwarding, router backup process and the process switching.

Packet forwarding:

In simple terms, packet forwarding is relaying of the available packets from one section of the internet to another by using nodes that are usually present in a computer’s network. These network packets are usually located in the OSI layer of the network layer and there are different patterns in which the packet forwarding is done, for that matter there are three patterns:

  • Unicast pattern

This pattern is considered to be the simplest one whereby the forwarding of the packet data is quite straight forward; the needed packet is usually relayed from one chain to another on a path that is described as from the source to the required destination. It is common in most of the network technologies like the internet.

  • Multicast pattern

It is usually common in the PIM system, the packet duplicated into several copies that are later on delivered to the required recipients presented as sets.

  • Broadcast pattern

This type requires the packets to be duplicated after which the copies are sent to multiple links and ensuring that every device on the network has received a copy. The idea is to only transfer copies on network devices that are within a certain broadcast domain. It is commonly found in the bridged Ethernet where there are different broadcast domains.

Packet forwarding only occurs when a decision has been made through the routing process especially in large networks since they are composed of many other networks that are linked together and for a message to transferred from one point to the other packet forwarding has to be applied. Due to its advances, packet forwarding has been introduced in other fields like the infrastructure that deals with wireless devices.

The Router lookup process:

There are several steps that the router hardware undergoes to test whether it’s sufficient to use in the routing process

Step 1-The router usually examines all the level one routes in order to find one that matches with the destination address of the required IP address. If the best match is an ultimate route, the route is used in packet forwarding and if the route found is a parent route then it proceeds to step two.

Step 2- The router examines a suitable subnet route for the parent route. If there is a match then packet forwarding takes place, if there is no match then the router proceeds to the next step.

Step 3- Testing the behavior of the router whether it has a class or classless. If it has a class then the lookup process is terminated and the packet is dropped, if it is classless then the process continues through searching from the routing table.

Step 4- If there is a slight match with the level one super network route then the router uses that route in packet forwarding.

Step 5- If there is no match among the routers on the routing table then the router drops the packet and aborts the process.

Process switching:

This process mostly occurs in operating systems that acquires control of a running process especially during the routing process. Interruptions are meant to occur during the switching process and as a result it is the duty of the operating system to detect the problem and after that it switches automatically switches from the interrupted process to the more secure process.

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