Lab Manual 05

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NATIONAL UNIVERSITY OF COMPUTER &
EMERGING SCIENCE

Computer Networks Lab (CL307)
Lab Session 05
Awais Ahmed || Faizan Yousuf || Munim Ali Khan
awais.ahmed@nu.edu.pk || faizan.yousuf@nu.edu.pk || munim.ali@nu.edu.pk

Application Layer Protocol
TELNET
A terminal emulation program for TCP/IP networks such as the Internet. The Telnet program
runs on your computer and connects your PC to a server on the network. You can then enter
commands through the Telnet program and they will be executed as if you were entering
them directly on the server console. This enables you to control the server and
communicate with other servers on the network. To start a Telnet session, you must log in to
a server by entering a valid username and password. Telnet is a common way to remotely
control Web servers. To telnet means to establish a connection with the Telnet protocol,
either with command line client or with a programmatic interface.
Let us apply Telnet on packet tracer.

Take the topology as in the above diagram. Set IPs on the PCs. As, by default, all PCs are in
vlan 1. We will create a virtual interface on switch with vlan 1 as follows.

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Now, we can ping to switch by our hosts because hosts are in vlan 1 and switch also has a
vlan 1 interface.

Now, try to telnet the switch from our PC, it refuses because we have not applied
authentication on the switch yet.

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So, let’s apply line authentication on the switch. The system supports 20 virtual tty (vty)
lines for Telnet, Secure Shell Server (SSH) and FTP services. Each Telnet, SSH, or FTP
session requires one vty line. You can add security to your system by configuring the
software to validate login requests.

Now, we can easily telnet. But it does not let us go in the switch enabled mode because
we have not set the password on the switch yet.

Let’s apply password on the switch enabled mode.

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Now, we can go inside Switch configuration mode from our pc.

SIMULATION
a) Now click on simulation icon in the right bottom of packet Tracer.
b) Now click on auto capture /play icon for packet capturing.
c) Click on the PC and go to Desktop Command Prompt then Telnet 192.168.1.1

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Now click on the TELNET packet show its header.
a) Shows OSI layers involved in transmission.
The popped up window (below) will enable you to trace the content of the
message through the OSI layer and what changes will occur at each layer (use
next and previous buttons to trace each layer content).

b) Show Inbound PDU Details.
The inbound tab shows the content of the message (header format) during the
receiving process.

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SSH
Secure Shell (SSH) is a cryptographic network protocol for secure data communication,
remote shell services or command execution and other secure network services between two
networked computers that connects, via a secure channel over an insecure network, a server
and a client (running SSH server and SSH client programs, respectively). It was designed as a
replacement for Telnet and other insecure remote shell protocols such as the Berkeley rsh
and rexec protocols, which send information, notably passwords, in plaintext, rendering them
susceptible to interception and disclosure using packet analysis. The encryption used by SSH
is intended to provide confidentiality and integrity of data over an unsecured network, such
as the Internet.
A network protocol that ensures a high-level encryption, allowing for the data transmitted over
insecure networks, such as the Internet, to be kept intact and integrate. SSH and SSH Telnet,
in particular, work for establishing a secure communication between two network-connected
computers as an alternative to remote shells, such as TELNET, that send sensitive information
in an insecure environment. In contrast to other remote access protocols, such as FTP, SSH
Telnet ensures higher level of connection security between distant machines but at the same
time represents a potential threat to the server stability. Thus, SSH access is considered a
special privilege by hosting providers and is often assigned to users only per request.
So, now let us apply SSH on the switch.

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Now, we try to telnet it but it is refused because ssh has over ruled telnet. So, we will use SSH protocol
on it. By default, username is admin.

And we can apply any sort of configuration on our switch from out pc.

Now, if we want to change the username from admin to something else, we will do it as follows.

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And from our pc as follows.

You can also see the generated keys in SSH as shown below.

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SIMULATION:
a) Now click on simulation icon in the right bottom of packet Tracer.
b) Now click on auto capture /play icon for packet capturing.
c) Click on the PC and go to Desktop Command Prompt then ssh -l admin 192.168.1.1

Now click on the SSH packet show its header.
b) Shows OSI layers involved in transmission.
The popped up window (below) will enable you to trace the content of the message
through the OSI layer and what changes will occur at each layer (use next and
previous buttons to trace each layer content).

b) Show Inbound PDU Details.
The inbound tab shows the content of the message (header format) during the receiving
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process.

Domain Name System
The Domain Name System (DNS) is a hierarchical distributed naming system for
computers, services, or any resource connected to the Internet or a private
network. It associates various information with domain names assigned to each of
the participating entities. Most prominently, it translates easily memorized domain
names to the numerical IP addresses needed for the purpose of locating computer
services and devices worldwide. The Domain Name System is an essential
component of the functionality of the Internet.
An often-used analogy to explain the Domain Name System is that it serves as the
phone book for the Internet by translating human-friendly computer hostnames into IP
addresses. For example, the domain name www.example.com translates to the
addresses 93.184.216.119 (IPv4) and 2606:2800:220:6d: 26bf:1447:1097:aa7 (IPv6).
Unlike a phone book, the DNS can be quickly updated, allowing a service's location on
the network to change without affecting the end users, who continue to use the same
host name. Users take advantage of this when they use meaningful Uniform Resource
Locators (URLs), and e-mail addresses without having to know how the computer
actually locates the services.
The Domain Name System distributes the responsibility of assigning domain names
and mapping those names to IP addresses by designating authoritative name servers
for each domain. Authoritative name servers are assigned to be responsible for their
supported domains, and may delegate authority over sub domains to other name
servers. This mechanism provides distributed and fault tolerant service and was
designed to avoid the need for a single central database. Some common DNS record
types are:

A record:
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The A record is one of the most commonly used record types in any DNS system. An
A record is actually an address record, which means it maps a fully qualified domain
name (FQDN) to an IP address. For example, an A record is used to point a domain
name, such as "google.com", to the IP address of Google's hosting server,
"74.125.224.147”. This allows the end user to type in a human- readable domain, while
the computer can continue working with numbers. The name in the A record is the
host for your domain, and the domain name is automatically attached to your name.

CNAME record:
Canonical name records, or CNAME records, are often called alias records because
they map an alias to the canonical name. When a name server finds a CNAME record,
it replaces the name with the canonical name and looks up the new name. This allows
pointing multiple systems to one IP without assigning an A record to each host name.
It means that if you decide to change your IP address, you will only have to change
one A record.

NS record:
An NS record identifies which DNS server is authoritative for a particular zone. The
"NS" stands for "name server". NS records that do not exist on the apex of a domain
are primarily used for splitting up the management of records on sub-domains.

SOA record:
The SOA or Start of Authority record for a domain stores information about the name
of the server that supplies the data for the zone, the administrator of the zone and the
current version of the data. It also provides information about the number of seconds
a secondary name server should wait before checking for updates or before retrying
a failed zone transfer.

Now using the DNS service on Server0.Go to server
services DNS First we add A record.

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Now click on Add.

Now add Cname record.

Now click on Add.

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Now go to pc5 Desktop web browser  type fast-cs and see how DNS works.

Start simulation.

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Click on DNS packet. See how DNS server resolved the name.

Now finally, required web page.

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a) Shows OSI layers involved in transmission.
The popped up window (below) will enable you to trace the content of the
message through the OSI layer and what changes will occur at each layer
(use next and previous buttons to trace each layer content).

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