WIA1005 Network Technology Foundation: Application Layer and Build A Small Network

WIA1005 Network
Technology Foundation
Chapter 6
Application Layer and Build a
Small Network
Contents
 Introduction
 Network Services
 Small Network
 Troubleshooting
Introduction
 The application layer is closest to the end user. The
layer that provides the interface between the applications
we use to communicate and the underlying network over
which our messages are transmitted.
 Application layer protocols are used to exchange data
between programs running on the source and
destination hosts.
 Some of the most widely known application layer
protocols include Hypertext Transfer Protocol (HTTP),
File Transfer Protocol (FTP), Trivial File Transfer
Protocol (TFTP), Internet Message Access Protocol
(IMAP), and Domain Name System (DNS) protocol.
Introduction
 The presentation layer has three primary functions:
 Formats, or presents, data from the source device into
a compatible form for receipt by the destination
device.
 Compression of the data in a way that can be
decompressed by the destination device.
 Encryption of the data for transmission and the
decryption of data upon receipt by the destination.
 The session layer create and maintain dialogs between
source and destination applications. The session layer
handles the exchange of information to initiate dialogs,
keep them active, and to restart sessions that are
disrupted or idle for a long period of time.
Network Services
 Hypertext Transfer Protocol (HTTP)
 This protocol transfers files that make up the web
pages of the World Wide Web.
 HTTP is a request/response protocol. When a client,
typically a web browser, sends a request to a web
server, The three common message types are GET,
POST, and PUT.
 The server will response according to the request.
 For secure communication across the Internet, the

HTTP Secure (HTTPS) protocol is used
Network Services
Network Services
 Email is a store-and-forward method of sending,
storing, and retrieving electronic messages across a
network. Email messages are stored in databases on
mail servers.
 Email clients communicate with mail servers to send and
receive email. Mail servers communicate with other mail
servers to transport messages from one domain to
another.
 Email supports three separate protocols for operation:
Simple Mail Transfer Protocol (SMTP), Post Office
Protocol (POP), and Internet Message Access Protocol
(IMAP).
Network Services
 Simple Mail Transfer Protocol (SMTP) transfers mail
reliably and efficiently. SMTP message formats require a
message header and a message body. When a client
sends email, the client SMTP process connects with a
server SMTP process on well-known port 25.
 Post Office Protocol (POP) enables a workstation to
retrieve mail from a mail server. With POP, mail is
downloaded from the server to the client and then
deleted on the server. The server starts the POP service
by passively listening on TCP port 110 for client
connection requests.
Network Services
Network Services
 Internet Message Access Protocol (IMAP) is another
protocol that describes a method to retrieve email
messages. However, unlike POP, when the user
connects to an IMAP-capable server, copies of the
messages are downloaded to the client application.
 The original messages are kept on the server until
manually deleted. Users view copies of the messages in
their email client software.
Network Services
 Domain names were created to convert the numeric IP
address into a simple, recognizable name.
 The Domain Name System (DNS) was created for
domain name to address resolution for these networks.
DNS uses a distributed set of servers to resolve the
names associated with these numbered addresses
 The DNS protocol defines an automated service that
matches resource names with the required numeric
network address. It includes the format for queries,
responses, and data.
 The DNS protocol uses a hierarchical system to create a
database to provide name resolution.
Network Services
 A DNS server provides the name resolution using the
Berkeley Internet Name Domain (BIND)
 The DNS server stores different types of resource
records used to resolve names. These records contain
the name, address, and type of record.
 A - An end device IPv4 address
 AAAA - An end device IPv6 address
 NS - An authoritative name server
 CNAME - Fully Qualified Domain Name
 MX - Mail exchange record; maps a domain name to a

list of mail exchange servers for that domain
Network Services
Network Services
Network Services
Network Services
 The Dynamic Host Configuration Protocol (DHCP)
service enables devices on a network to obtain IP
addresses and other information from a DHCP server.
 This service automates the assignment of IP addresses,
subnet masks, gateway, and other IP networking
parameters.
Network Services
 The File Transfer Protocol (FTP) is another commonly
used application layer protocol. FTP was developed to
allow for data transfers between a client and a server.
 An FTP client is an application that runs on a computer
that is used to push and pull data from a server running
an FTP daemon (FTPd).
Network Services
 The Server Message Block (SMB) is a client/server file
sharing protocol to describe the structure of shared
network resources, such as directories, files, printers,
and serial ports. It is a request-response protocol.
 SMB messages can:
 Start, authenticate, and terminate sessions
 Control file and printer access
 Allow an application to send or receive messages to

or from another device
Network Services
Small Network
 The design of a small network is usually simple. The
number and type of devices included are significantly
reduced compared to that of a larger network.
 There are a number of factors that need to be
considered when implementing a small network:
 Cost
 The device capacity includes the number and types

of ports
 Speed
 Bandwidth
 Expandability
 Fixed / Modular
 Services
Small Network
 Another important part of network design is reliability.
Even small businesses often rely heavily on their
network for business operation. A failure of the network
can be very costly. In order to maintain a high degree of
reliability, redundancy is required in the network design.
 Besides, the types of application and traffic treatment
must be identified.
 The common applications include Web, Email, FTP,
DHCP, DNS, and SSH.
Small Network
Small Network
 Network administrator needs to plan for the growth of the
small network.
 To scale a network, several elements are required:
 Network Documentation
 Device Inventory
 Budget
 Traffic Analysis
 Type of traffic
 Utilization
Small Network
 Network administrator needs to secure the network from
attacks.
 Vulnerability is the degree of weakness which is
inherent in every network and device.
 There are three primary vulnerabilities:
 Technological
 Configuration
 Security policy
 An equally important vulnerability is the physical security

of devices.
Small Network
 Malware is code or software that is specifically designed
to damage, disrupt, steal, or perform illegitimate action
on data, hosts, or networks.
 Viruses
 Worms
 Trojan horses
 Network Attacks
 Reconnaissance attacks
 Access attacks
 Denial of service
Small Network
 Keeping up-to-date with the latest developments can
lead to a more effective defense against network attacks.
 Authentication, authorization, and accounting (AAA) is
the primary framework to set up access control on a
network device.
 A firewall can be used to protect users from external
threats.
 To protect network devices, it is important to use strong
passwords. Blocking login attempt is required against
brute-force attack.
 security passwords min-length
 login block-for 120 attempts 3 within 60
Troubleshooting
 Troubleshooting is used to analyse the problem,
determine the cause of the error, implement a plan of
action, and resolve the network issue.
Troubleshooting
 When a problem has been solved and a solution
implemented, it is important to verify the system
operation. ping, traceroute and show are some of the
verification commands
 ping command is an effective way to test connectivity.
The ping command uses the Internet Control Message
Protocol (ICMP) and verifies Layer 3 connectivity.
Troubleshooting
 Traceroute is useful in troubleshooting routing loops and
determining the exact next-hop router.
 An ICMP "time exceeded" indicates that a router in the
path has seen and discarded the packet. An ICMP
"destination unreachable" indicates that a router has
received the packet, but discarded it because it could not
be delivered.
Troubleshooting
 The show commands display relevant information about
the configuration and operation of the device.
 show running-config
 show interfaces / show ip interface
 show arp
 show ip route
 show protocols
 show version
 The ipconfig or ipconfig /all commands are used to

view IP address.
 The arp –a command lists all devices in ARP cache.
Troubleshooting
 The IOS debug command provides valuable information
when troubleshooting or verifying system operations.
 All debug commands are entered in privileged EXEC
mode. The filter command is used to include only the
relevant information.
 Commands such as debug all or debug ip packet a
generate a substantial amount of output.
 Disable the debugging process when enough data has
been captured:
 no debug
 undebug
 undebug all
Troubleshooting
Troubleshooting
 Administrative can access to a router remotely on virtual
console (VTY) lines using SSH or Telnet. However, log
messages are not displayed by default on virtual console
lines.
 To display log messages on a terminal (virtual console)
 terminal monitor
 To stop logging messages on a terminal

 terminal no monitor

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WIA1005 Network

 For secure communication across the Internet, the

 AAAA - An end device IPv6 address

 NS - An authoritative name server

 CNAME - Fully Qualified Domain Name

 MX - Mail exchange record; maps a domain name to a

 Control file and printer access

 Allow an application to send or receive messages to

 The device capacity includes the number and types

 An equally important vulnerability is the physical security

 show interfaces / show ip interface

 The ipconfig or ipconfig /all commands are used to

 To stop logging messages on a terminal

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