Introduction to Computer Network Protocols

The word protocol is derived from the Greek word “protocollon” which means a leaf of paper glued to manuscript volume. In computer protocols means a set of rules, a communication language or set of standards between two or more computing devices. Protocols exist at the several levels of the OSI (open system interconnectivity) layers model. In the telecommunication system, there are one more protocols at each layer of the telephone exchange. On the internet, there is a suite of the protocols known as TCP/IP protocols that are consisting of transmission control protocol, internet protocol, file transfer protocol, dynamic host configuration protocol, Border gateway protocol and a number of other protocols.

In the telecommunication, a protocol is set of rules for data representation, authentication, and error detection. The communication protocols in the computer networking are intended for the secure, fast and error free data delivery between two communication devices. Communication protocols follow certain rules for the transmission of the data.

Protocols Properties

Different protocols perform different functions so it is difficult to generalize the properties of the protocols. There are some basic properties of most of the protocols.

• Detection of the physical (wired or wireless connection)

• Handshaking

• How to format a message.

• How to send and receive a message.

• Negotiation of the various connections

• Correction of the corrupted or improperly formatted messages.

• Termination of the session.

The widespread use of the communication protocols is a prerequisite to the internet. The term TCP/IP refers to the protocols suite and a pair of the TCP and IP protocols are the most important internet communication protocols. Most protocols in communication are layered together where the various tasks listed above are divided. Protocols stacks refer to the combination of the different protocols. The OSI reference model is the conceptual model that is used to represent the protocols stacks. There are different network protocols that perform different functions. Following is the description of the some of the most commonly used protocols.

HTTP (Hyper Text Transfer Protocol)

Hypertext transfer protocol is a method of transmitting the information on the web. HTTP basically publishes and retrieves the HTTP pages on the World Wide Web. HTTP is a language that is used to communicate between the browser and web server. The information that is transferred using HTTP can be plain text, audio, video, images, and hypertext. HTTP is a request/response protocol between the client and server. Many proxies, tunnels, and gateways can be existing between the web browser (client) and server (web server). An HTTP client initializes a request by establishing a TCP connection to a particular port on the remote host (typically 80 or 8080). An HTTP server listens to that port and receives a request message from the client. Upon receiving the request, server sends back 200 OK messages, its own message, an error message or other message.

POP3 (Post Office Protocol)

In computing, e-mail clients such as (MS outlook, outlook express and thunderbird) use Post office Protocol to retreive emails from the remote server over the TCP/IP connection. Nearly all the users of the Internet service providers use POP 3 in the email clients to retrieve the emails from the email servers. Most email applications use POP protocol.

SMTP (Simple Mail Transfer Protocol)

Simple Mail Transfer Protocol is a protocol that is used to send the email messages between the servers. Most email systems and email clients use the SMTP protocol to send messages to one server to another. In configuring an email application, you need to configure POP, SMTP and IMAP protocols in your email software. SMTP is a simple, text based protocol and one or more recipient of the message is specified and then the message is transferred. SMTP connection is easily tested by the Telnet utility. SMTP uses the by default TCP port number 25

FTP (File Transfer Protocol)

FTP or file transfer protocol is used to transfer (upload/download) data from one computer to another over the internet or through or computer network. FTP is a most commonly communication protocol for transferring the files over the internet. Typically, there are two computers are involved in the transferring the files a server and a client. The client computer that is running FTP client software such as Cuteftp and AceFTP etc initiates a connection with the remote computer (server). After successfully connected with the server, the client computer can perform a number of the operations like downloading the files, uploading, renaming and deleting the files, creating the new folders etc. Virtually operating system supports FTP protocols.

IP (Internet Protocol)

An Internet protocol (IP) is a unique address or identifier of each computer or communication devices on the network and internet. Any participating computer networking device such as routers, computers, printers, internet fax machines and switches may have their own unique IP address. Personal information about someone can be found by the IP address. Every domain on the internet must have a unique or shared IP address.

DHCP (Dynamic Host Configuration Protocol)

The DHCP or Dynamic Host Configuration Protocol is a set of rules used by a communication device such as router, computer or network adapter to allow the device to request and obtain and IP address from a server which has a list of the larger number of addresses. DHCP is a protocol that is used by the network computers to obtain the IP addresses and other settings such as gateway, DNS, subnet mask from the DHCP server. DHCP ensures that all the IP addresses are unique and the IP address management is done by the server and not by the human. The assignment of the IP addresses is expires after the predetermined period of time. DHCP works in four phases known as DORA such as Discover, Observe, Request and Authorize

IMAP (Internet Message Access Protocol)

The Internet Message Access Protocol known as IMAP is an application layer protocol that is used to access to access the emails on the remote servers. POP3 and IMAP are the two most commonly used email retrieval protocols. Most of the email clients such as outlook express, thunderbird and MS outlooks support POP3 and IMAP. The email messages are generally stored on the email server and the users generally retreive these messages whether by the web browser or email clients. IMAP is generally used in the large networks. IMAP allows users to access their messages instantly on their systems.

ARCNET

ARCNET is a local area network technology that uses token bus scheme for managing line sharing among the workstations. When a device on a network wants to send a message, it inserts a token that is set to 1 and when a destination device reads the message it resets the token to 0 so that the frame can be used by another device.

FDDI

Fiber distributed data interface (FDDI) provides a standard for data transmission in a local area network that can extend a range of 200 kilometers. The FDDI uses token ring protocol as its basis. FDDI local area network can support a large number of users and can cover a large geographical area. FDDI uses fiber optic as a standard communication medium. FDDI uses dual attached token ring topology. A FDDI network contains two token rings and the primary ring offers the capacity of 100 Mbits/s. FDDI is an ANSI standard network and it can support 500 stations in 2 kilometers.

UDP

The user datagram protocol is a most important protocol of the TCP/IP suite and is used to send the short messages known as datagram. Common network applications that uses UDP are DNS, online games, IPTV, TFTP and VOIP. UDP is very fast and light weight. UDP is an unreliable connectionless protocol that operates on the transport layer and it is sometimes called Universal Datagram Protocol.

X.25

X.25 is a standard protocol suite for wide area networks using a phone line or ISDN system. The X.25 standard was approved by CCITT now ITU in 1976.

TFTP

Trivial File Transfer Protocol (TFTP) is a very simple file transfer protocol with the very basic features of the FTP. TFTP can be implemented in a very small amount of memory. TFTP is useful for booting computers such as routers. TFTP is also used to transfer the files over the network. TFPT uses UDP and provides no security features.

SNMP

The simple network management protocol (SNMP) forms the TCP/IP suite. SNMP is used to manage the network attached devices of the complex network.

PPTP

The point to point tunneling protocol is used in the virtual private networks. PPP works by sending regular PPP session. PPTP is a method of implementing VPN networks.

OTHER PROTOCOLS

VTP, ARP, IPX, OSPF, RARP, NFS, BOOTP, NNTP, IRC, RADIUS, Soap, Telnet, RIP, SSH.

DHCP Overview

In this section you will learn the DHCP router overview, dynamic host configuration protocol overview, network tutorials, troubleshooting tips, subnetting, IP addressing. DHCP or Dynamic Host Configuration Protocol is a network protocol, which is configured in such a way that is provides the IP addresses to the network computers automatically. There is no need to assign the IP address to the client computers individually. DHCP assigns the IP addresses from the given range of the numbers also called DHCP scope.

On the other end, client computers are configured in such a way that they get the IP addresses automatically from the DHCP server during the boot up process. Additionally, DNS and WINS servers can also be configured with the DHCP server.

When a computer starts up it gets the IP addresses from the DHCP server from the defined pool of addresses.

The assigning of the IP address by the DHCP server can be categorized as follows

1. A user turns on the computer with the DHCP client enabled on it.
2. The client PC sends broadcast request (known as DHCP DISCOVER) and then look for the DHCP server to answer.
3. The DHCP server receives the DISCOVER packet and based on the availability and defined settings, the server choose any available IP address and then give to the client. Then DHCP server sends back to the client with DHCP OFFER with that available address information.
4. Again client sends a request to DHCP server known as DHCP REQUEST, in which it lets the server know that it is using the address offered by the DHCP.
5. The DHCP server then again send a acknowledgement to the client known as DHCP ACK, in which it confirm the client that the specific IP address has been assigned to it for a given period of time.

This process of assigning the IP addresses by the DHCP server also known as DORA (Discover, Offer, Request, and Acknowledgement).

When a computer uses a static IP address there can be the chances of error and conflict when two computers use the same IP address. By using the DHCP server there are no chances of such kind of conflicts and errors.

Along with the IP addresses, the DHCP server also enables the client computers to extract all the settings and configurations from the DHCP server on an IP network. These settings include the Firewall, Router, DNS, NAT, WINS, Gateway and Subnet masks settings.

The overall purpose of the DHCP server is to reduce the workload and error margins, which can occur in assigning the IP addresses manually.

The IP address assigned by the DHCP server is for the limited or leased period of time and if a client needs an to extend that leased period for the IP address then client must send a extension request to the DHCP server before this period expires. If the client do not send an extension request, then this IP address becomes free on expiration and is assigned to another client. If a user wants to change the IP address given by the DHCP server then he/she do it by giving these commands on the command prompt.

“IPconfig/release then IPconfig/renew”.

This command will remove the current IP address and assign a new IP address to the client.

There can also be some reserved addresses based on the MAC address or hostname of the client. These reserved addresses are fixed addresses and can only be assigned to the fixed clients.

How to Setup a DHCP Server?

The installation of the DHCP server in the Windows 2000 or Windows 2003 is quite easy. You can install the DHCP server by using the “Manager Your Server Wizard”.

Open Manager Your Server wizard and select the DHCP server option and press next then you will be asked to enter the name and the description of the DHCP scope.

A scope is a collection of the IP addresses on subnet that use DHCP. In the next window you will be asked to define the range of the IP addresses and the appropriate subnet mask that DHCP server will distribute across the all network. Next you will see a window in which you can add anyIP address, which they don’t want to use because these are already in use for example 100.100.100.10 is an IP address of the company’s router and you don’t want that DHCP server use this address and assign to some other client.

So you can add these addresses in the exclusion field. You can define fix range of the IP addresses for exclusion. In the next step you have to assign the lease duration this means that for how long a client can use the IP address, which it got from the DHCP server. You can assign any lease duration. 10 hours, 1 week, 1 month or 1 year so on.

Next you will be asked to configure the scope of the DHCP options now or you can also configure it later.

Next the DNS and the domain name configurations and settings can be entered. The IP address of the DNS server will be assigned and distributed by the DHCP server.

Next if you have WINS requirements then you can enter the IP address of the WINS server. You can just type the server name into the box and then press resolve it will automatically resolve the name of server and find the IP address.

The next step is to activate the scope in the DHCP server because the DHCP server will not work until and unless you activate the scope. The DHCP server is now installed and you can modify the settings according the structure and the requirements of your network.

Make a plan according to the needs of your network before using the DHCP server.