Introduction to Routing and Packet Switching Networks

• Inside the Router
  
• CLI Configuration and Addressing
  
• Building the Routing table
  
• Path Determination and switching Functions

Objective

• Identify a router as a computer with an OS and hardware designed for the routing process.
  
• Demonstrate the ability to configure devices and apply addresses.
  
• Describe the structure of a routing table.
  
• Describe how a router determines a path and switches packets
  

Introduction

Router as a computer

The basic purpose of a router is to route in and out from the source of information to its destination with specific addresses. Route works as computers that focus and specific in sending packets of data over the data network across the globe. Route have a special task and responsible for the purpose of interconnecting among networks by choosing the best path or route for a packet data to travel and forwarding packet data to their destination. Router is just like a postmaster of the network, where all needed information is available to the journey of the packet data from its source to its destination.

Routers works as the network center where all related information must pass through a specific route to ensure all packets data will be forwarded for its source to its destination correctly. In general routers have 2 obvious connections:

• WAN connection (involve public ISP)
  
• LAN connection

The main purpose of this router in the network is to ensure and examine the entire data packet's passes through its and verify all of the data packets destination IP address, and finally determines the finest path by obtain the assist of a routing table. This mean that the final route will be determines by the most reliable route of the routing table.

Inside the Router

The inside of a router is most likely least that mother board of a computer system. It consists of CPU, ROM, RAM, NVRAM, Flash memory and Interfaces. The design of a router maybe different from one manufacturing to other manufacturing company but the basic component is almost the same.

Inside the Router

In most routers the interface types and function are almost the same:

• Ethernet / fast Ethernet interfaces
  

• Serial interfaces
  
• Management interfaces
  

This interfaces have different function due to different application of devices connected the router.

Router Bootup Process

The bootup of a router is just similar to a computer. Systemic process is used by the router when its bootup. What happen here is just like a computer will sequence bootup form one devices to other devices. This including testing the software , hardware, operating system.

Bootup Process

The major phases to the router boot-up process are router will test and check the router hardware. The router will test router hardware. The bootup process usually started with Power-On Self Test (POST), Loading the Bootstrap program &

Executing bootstrap loader, Locate & load Cisco IOS software –Locate the IOS & cconfiguration File and Loading the IOS and finally locating & loading startup configuration file or enter setup mode. At this point the bootstrap program appears for the configuration file. In some cases when the startup configuration file can not be found, the router automatically wills the user to enter setup mode. This setup mode will provided the most basic configuration information about the router.

Main Step of the Bootup Process for a router (Cisco router) :

POST ( Power On Self Test)

Loading the Bootstrap program

Locating Cisco IOS

Loading Cisco IOS

Locating the Configuration File

Loading the Startup Configuration File or Entering Setup Mode

After all processes involve with the bootup is ready , router will proceed to the next level of process for validating the router boot-up process:

The show version command is used to view information about the router during the bootup process. Information includes:

Building the Routing Table

The main purpose of a router is to forward the data packet to its destination according to the destination IP address. This process can be done if the router has all the required information stored in its routing table. Routing table will provided the best information of the path available to the data packets destination.

Routing table

Routing table is a random access memory (RAM) that capable to accumulate important information related to the best path destination of the data packets. This information is useful for the router before forwarding the data packet, this include the directly connected and remote or adjacent network, next hop that represent another router in the network.

Router A is directly connected to Router B and Router C is remotely connected. In this case Router C can be the net hop outgoing or exit interface of Router A before reach the final destination.

Always, remember that when dealing with the router is careful of the router interfaces. This is because wrong configuration on the interface will cause your nightmare on troubleshooting a faulty network.

There three important in understanding the connection of a route:

1. Directly connected routes – All neighbour or nearest or next door routers connection is directly connected to the route interface.
   

1. Static Router – A single path for the router to send or received the packets data among routers.
   
2. Dynamic router – The option that being provide by the router to choose any new path at any point in order to reach its destination.
   

The routing table of a router can be display with # show ip route command.

We can see that there is no static and dynamic routing protocol is used. Only the directed connected protocol is used.

• C: represent a directly connected route
  
• 198.198.1.0, show the network address of the directly connected route
  
• Ethernet 0 and Serial 0 are the interface being used to reach this network.
  

Directly Connected Network

The concept of host, network and subnet mask is important in designing a network. As we know computer or network devices usually only has a single interface e.g. NIC compare to router. Router was purposely design to have multiple interface, the most simple router have two interface the serial , S0 and Ethernet , E0. In dealing with configuration of a network, the ideal of network address and host address is important. Also remember that host is subset of network in IP addressing.

From this diagram, if we configure PC 1 to 198.198.1.2 and subnet 255.255.255.0, now PC1 become a member of 198.198.1.0/24 network. This also happens to Ethernet interface, E0, e.g. we configure with 198.198.1.1. But for serial interface, S0, the interface is member of the next network, 198.198.2.0. The network 198.198.1.0 and 198.198.2.0 is different network. To active the configured data of the network the command no shut is applied.

Static and dynamic route usually be configure after the existing of directly connected route. The directly connected have to be configure first and it just to be come mandatory to have directly connected route in a router before any routing can be done.

Static Routing

The main function of static routing and dynamic routing protocol are to enable remote network in to the routing table of existing router. Static router consist of network address and subnet mask of the remote network.

Static routing usually applied to a network with few routers, connection to internet with single ISP and a large network with hub and spoke topology.

Dynamic Routing

Same as static routing , dynamic routing also can de added in the routing table. The earliest dynamic routing is the routing information protocol (RIP).

Dynamic routing protocols provide important information regarding the network. The most typical information activities are network discovery and updating and maintaining routing tables' information. Dynamic routing protocol share information of known network among routers that using the same routing protocol. Dynamic routing protocol also can learn any networks that are connected via other routers. Some of dynamic routing protocol are RIP, IGRP, EIGRP, OSPF, IS-IS and BGP.

Routing Table Principle

Path Determination and Switching Functions

In this section we wile learn how that data packet is travelling from one hop to another hop until it reach it destination. This will include how the frame field change in their journey.