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Session 3 (a) - Unit 9 - Computer Networks protocols

Network standards and protocols, importance of different protocols.
by

Masudur rahman

on 12 February 2014

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Transcript of Session 3 (a) - Unit 9 - Computer Networks protocols

Surprises!
FTP
But HTTP is not secured..
Solution is SHTTP
How does DNS work?
Network Protocols & Standards
+
Virtual Ports for communication
DNS Service and Protocol
WWW and HTTP Services
Which product do you
want
to buy?
HTTP specifies a request/response protocol. When a client, typically a web browser, sends a request message to a server, the HTTP protocol defines the message types the client uses to request the web page and also the message types the server uses to respond. The three common message types are GET, POST, and PUT. GET is a client request for data. A web browser sends the GET message to request pages from a web server. POST and PUT are used to send messages that upload data to the web server. PUT uploads resources or content to the web server.
Domain Name System (DNS) is a client/server service is different from the other client/server services that we are examining. While other services use a client that is an application (such as web browser, e-mail client), the DNS client runs as a service itself. The DNS client, sometimes called the DNS resolver. Computer operating systems also have a utility called nslookup that allows the user to manually query the name servers to resolve a given host name.
The e-mail server operates two separate processes:
Mail Transfer Agent (MTA)
Mail Delivery Agent (MDA)

The Mail Transfer Agent (MTA) process is used to forward e-mail. As shown in the figure, the MTA receives messages from the MUA or from another MTA on another e-mail server. Based on the message header, it determines how a message has to be forwarded to reach its destination. If the mail is addressed to a user whose mailbox is on the local server, the mail is passed to the MDA. If the mail is for a user not on the local server, the MTA routes the e-mail to the MTA on the appropriate server.
A DNS server provides the name resolution using the name daemon. The DNS server stores different types of resource records used to resolve names. These records contain the name, address, and type of record.
Some of these record types are:
A - an end device address
NS - an authoritative name server
CNAME - the canonical name (or Fully Qualified Domain Name) for an alias; used when multiple services have the single network address but each service has its own entry in DNS
MX - mail exchange record; maps a domain name to a list of mail exchange servers for that domain
How DNS Works?
Everbody likes to laugh...
use humor
By end of this session we will be able to describe different network standards and protocols (DNS, DHCP, IP HTTP, FTP, SMTP, POP3) along with the importance of each of these. We also will be able to configure client compter, DNS server, DHCP server and testing the connectivity.
Time for practical activity
How to protect the organisation from these threats?
EMail Services - SMTP & POP3 Protocol
Two example Application layer protocols are Post Office Protocol (POP) and Simple Mail Transfer Protocol (SMTP). When people compose e-mail messages, they typically use an application called a Mail User Agent (MUA), or e-mail client. The MUA allows messages to be sent and places received messages into the client's mailbox, both of which are distinct processes.

In order to receive e-mail messages from an e-mail server, the e-mail client can use POP. Sending e-mail from either a client or a server uses message formats and command strings defined by the SMTP protocol. Usually an e-mail client provides the functionality of both protocols within one application.
What is an IP address?
How the IP address works?
Port numbers identify applications and Application layer services that are the source and destination of data. Server programs generally use predefined port numbers that are commonly known by clients.
Domain Name System (DNS) - TCP/UDP Port 53
Hypertext Transfer Protocol (HTTP) - TCP Port 80
Simple Mail Transfer Protocol (SMTP) - TCP Port 25
Post Office Protocol (POP) - TCP Port 110
Telnet - TCP Port 23
Dynamic Host Configuration Protocol - UDP Ports 67 and 68
File Transfer Protocol (FTP) - TCP Ports 20 and 21
Virtual Communication Ports
Try the command ipconfig /displaydns which will show you the cached DNS
The Domain Name System uses a hierarchical system to create a name database to provide name resolution. The hierarchy looks like an inverted tree with the root at the top and branches below.
At the top of the hierarchy, the root servers maintain records about how to reach the top-level domain servers, which in turn have records that point to the secondary level domain servers and so on.
Top level domain

au - Australia
.co - Colombia
.com - a business or industry
.jp - Japan
.org - a non-profit organization
When a web address (or URL) is typed into a web browser, the web browser establishes a connection to the web service running on the server using the HTTP protocol. URLs (or Uniform Resource Locator) and URIs (Uniform Resource Identifier) are the names most people associate with web addresses. To better understand how the web browser and web client interact, we can examine how a web page is opened in a browser. For this example, we will use the URL: http://www.cisco.com/web-server.htm. First, the browser interprets the three parts of the URL:
1. http (the protocol or scheme)
2. www.cisco.com (the server name)
3. web-server.htm (the specific file name requested).
The browser then checks with a name server to convert www.cisco.com into a numeric address, which it uses to connect to the server. Using the HTTP protocol requirements, the browser sends a GET request to the server and asks for the file web-server.htm. The server in turn sends the HTML code for this web page to the browser. Finally, the browser deciphers the HTML code and formats the page for the browser window.
Hyper Text Transfer Protocol
The File Transfer Protocol (FTP) is another commonly used Application layer protocol. FTP was developed to allow for file 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 files from a server running the FTP daemon (FTPd).

To successfully transfer files, FTP requires two connections between the client and the server: one for commands and replies, the other for the actual file transfer.

The client establishes the first connection to the server on TCP port 21. This connection is used for control traffic, consisting of client commands and server replies. The file transfer can happen in either direction. The client can download (pull) a file from the server or, the client can upload (push) a file to the server.
Dynamic Host Configuration Protocol
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.

DHCP allows a host to obtain an IP address dynamically when it connects to the network. The DHCP server is contacted and an address requested. The DHCP server chooses an address from a configured range of addresses called a pool and assigns ("leases") it to the host for a set period.
How DHCP Works?
SMB Protocol
With P2P applications based on the Gnutella protocol, people can make files on their hard disks available to others for downloading. Gnutella-compatible client software allows users to connect to Gnutella services over the Internet and to locate and access resources shared by other Gnutella peers.

Many client applications are available for accessing the Gnutella network, including: BearShare, Gnucleus, LimeWire, Morpheus, WinMX and XoloX (see a screen capture of LimeWire in the figure). While the Gnutella Developer Forum maintains the basic protocol, application vendors often develop extensions to make the protocol work better on their applications.
Lets do configure IP address manually and by using
Recap of today's session: Different types of protocols which work in Application Layer
Find out the IP Address and MAC Address of a computer
We will learn how to build a network by using iNetwork Simulator and we will complete P2 M1 task.
Recap of last session (OSI model, TCP IP protocol)
Lets configure IP address of "work station"
Connect 2 work stations
Test the connectivity of the network by using DOS command.
Use iNetwork Simulator to simulate a computer network
What are the problem using static IP address?
Configure and test DHCP server
Configure and test DNS server
Full transcript