A Introduction To Computer Networks

Published Date: 02 Nov 2017

This report mainly discusses about two major topics in computer networks, Internet Protocol Addressing and Dynamic Routing Protocol (RIP). Also we are going to discuss about the concepts of sub-netting and VLSM, which are the most important topics in the networking world. In addition to this we discuss about the versions of Routing Information Protocol

1.1 Introduction to Labs

The first course, Introduction to Computer Networks has five labs. Each labs session provided us the basic information to handle and work on networking devices, which are more important in networking field. It also provided hands on experience towards all the equipments.

1.2 Objectives

The main objective of this lab is to provide sound knowledge of fundamentals relating to the networks where most important concepts are covered both in theory and practical. In OSI model, the functions of Network layer as how router connects and routes two different networks are explored and also importance of dynamic routing is explained. Moreover, the lab clearly elaborates the concept of sub-netting and VLSM.

1.3 Laboratories Achievements

During the five labs, my-self and my group members configured the high-end routers available in the equipment room. This gave us deep knowledge about these devices and what they are capable of doing. We also used sniffer PC`s to get a clear picture of how the encapsulation process happens during packet transfer.

1.4 Outline

The material in this report is organised into four chapters and appendices. The chapters deal with the following topics:

Chapter 2: IP Addressing

Chapter 3: Routing Information Protocol

Chapter 4: Conclusion

CHAPTER 2

2 IP Addressing

This chapter focuses on a detailed over-view of IP addressing scheme, IP classes and IP services to meet network requirements. Further this chapter breaks down the idea of sub-netting and VLSM (variable length subnet mask) concepts which are on top of the stack.

2.1 IP OVER-VIEW

IP address or internet protocol addressing is a name or a label given to network devices via which a device or a host communicates with other devices. IP address is an address in the real sense of the term. IP address is represented in dotted decimal notation. Each decimal number represents one octet (8-bits). However, the TCP / IP sees the IP address in binary form. The IP address is 32-bits. Therefore 232 combinations of IP addresses are possible. The IP address is divided into 4 octets each of which is 8-bits.

Figure 2.1 Dotted Decimal System representation

The above diagram represents the Dotted Decimal representation of IP addressing scheme. Each blocks in the figure 2.1 are filled with 0’s or 1’s which depends upon the IP Address. IP version 4 addressing scheme can address up to 232 = 4294967296 unique hosts. IANA- Internet Assigned Numbers Authority controls numbers for protocols, the Country Code Top Level Domains and maintains the IP Address allotments.

IP address is a combination of Network address and Host address.

IP = Network ID + Host ID

SUMMARY OF CLASSES

Figure 2.2 SUMMARY OF CLASSES

2.2 IP Classes

IP address is classified into five different classes as mentioned in the above diagram 2.1.

Class

Range

Subnet mask

Network

Host

Class – A

0-126

255.0.0.0

27-2

224 – 2

Class – B

128-191

255.255.0.0

214-2

216 – 2

Class – C

191-223

255.255.255.0

221-2

28 – 2

Class – D

224-239

255.255.255.255

Reserved for Multicast

Class – E

Research purpose

Table 2.1 IP Classes in brief

Table 2.1 shows the IP Address classes and its range. A Class A network address, the first byte is assigned to the network address and the three remaining bytes are used for the node address. Similarly a Class B and Class C network address, the first two and three bytes are assigned to the network address and the remaining two and one bytes are used for the node address respectively.

Reason for -2 in the Network ID:

The two combinations all 0's and all 1's are not valid because they are reserved for some functions mentioned below.

All 1's in class A Network ID produces 127.0.0.0, which is a Loop back Network. 127.0.0.1 - Loop back address used for trouble shooting purpose.

All 0's combination represents " ANY ", which means 0.0.0.0

Reason for -2 in the Host ID:

Here again two combinations are not valid since it is reserved for some functions mentioned below.

All 1's in the Host portion represents a broadcast. Example: 10.255.255.255 (Class A).

2. All 0's in the Host portion represents an entire network. Example: 10.0.0.0 (Class A).

2.3 Subnet Masks

A subnet mask is a logical division of an IP address into network and host portion. By making all network bits as "1" and all host bits as "0", a subnet mask can be generated.

2.4 Subnetting

Subnetting is made use when we want to take one network address and create smaller network groups. It is a process of logically dividing the network address of an IP into subnets. The technique behind sub-netting is borrowing or stealing the bits from the host position. The number of bits depends on the number of subnets. This breaks the single broadcast domain into smaller broadcast domain.

Why do we go for sub-netting?

Less IP wastage.

Single broadcast domain is divided into smaller broadcast domain.

Reduces the number of system unnecessarily receiving and processing packets.

Example:

192.168.100.41/27 – Here /27 denotes the number of 1 bits occupied by the network portion. In the above example 23 = 8 sub-networks can be created and 25-2 = 32 hosts can be accommodated in each of the 8 subnets.

Here, 192.168.100.0 represents the network address and 192.168.100.255 denotes the broadcast IP of the 192.168.100.0 network.

Variable-Length Subnet Masks (VLSM)

When a subnetted network is further subdivided to form sub-nets it is called as VLSM (Variable-length subnet mask). VLSM avoids wastage of IP address. And also it provides scalability i.e. if we add a new branch office we need not change all the subnets.

VLSM1

Figure 3.1 Implementation of VLSM

2.5 IP Version 6

IPv6 is an enhancement of IPv4. IPv6 is 128 bits in length. Therefore 2128 address are possible. It is expressed in Colon Hexa Decimal System. It provides more security. IPv6 was developed to overcome the bottle neck problems of IPv4.

Address exhaustion problem.

Provides better performance.

Improved management.

More secure.

2.6 Summary

IP address is a name or a label given to network devices via which a device or a host communicates with other devices. To divide networks into different smaller groups sub-netting and VLSM are used. IPv6, advancement of IPv4 makes the installation of network layer simple.

CHAPTER 3

3 ROUTING INFORMATION PROTOCOL

3.1 Introduction:

Routing Information Protocol is the abbreviation of RIP. RIP is a dynamic routing protocol. It advertises its network dynamically to all other connected networks. There are other dynamic routing protocols namely

RIP

OSPF

IGRP

The dynamic routing protocols itself is classified into two categories namely

DISTANCE VECTOR ROUTING

LINK STATE ROUTING

Dynamic routing protocols choose a route based upon some parameters. When the parameters are based on the number of hops in the network it is termed as Distance vector routing. Examples of Distance vector routing are Routing Information Protocol, Border Gateway Protocol etc. When the parameters are based on certain metric it is termed as Link State routing. Examples of link state routing are Enhanced interior gateway routing protocol, Open shortest path first etc.

Table 3.1 Distance vector routing vs link-state routing

S.no

Link state routing

Distance Vector routing

1.

They are partial. i.e. LSA that are affected by the topological change are sent

They are partial. i.e. sends all the routes all the time.

2.

Relationship is established with neighbouring router

No relationship is established with the neighboring routers

3.

Sends updates about the link in form of LSA- Link state advertisement.

Sends updates about the network ID’s itself.

3.1.1 Timers:

Periodic updates are exchanged in Distance vector routing protocol. RIP keeps account of timers. the timers of RIP are as follows

Update timer : every 30 seconds

Invalid timer : 180 seconds

Hold down timer : 180 seconds

Flush timer : 240 seconds

3.1.2 Route poisoning:

RIP protocol will send a flash update as metric 16 when a network is down, denoting that the network is unreachable. This is called as route poisoning. Poison reverse is an acknowledgement for route poisoning.

RIPv1 vs RIPv2

RIPv1 is a simple dynamic routing protocol that sends flooded broadcast packets to advertise its network. RIPv2 is an advancement or enhancement of the version 1. The RIPv2 supports classless inter domain concept. They both make use of BELLMAN FORD algorithm.

3.3 Summary

RIP is popularly used dynamic routing protocol. The RIPv1 can only support up to 15 hops. This is a major limitation of RIPv1. The bottle neck problems of RIPv1 were resolved in RIP v2 with further more enhancements. RIP makes use Dijkstra algorithm to find the best available route in the network.

CHAPTER 4

4 CONCLUSIONS AND References

4.1 Conclusions

I gained immense knowledge in the networking environment through the various router configurations and by knowing the various types of cables and connectors. The labs in the first course provided me in depth knowledge about the intricate concepts in a simple way. The IP addressing lab brought an exposure to IP addressing scheme, Sub-netting, VLSM etc. In routing information protocol lab, I configured routers using dynamic routing protocols and tested its connectivity by pinging to the remote end router.