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LAB SESSION: 1

Introduction to Network Programming

When writing programs that communicate across a computer network, one must first

invent a protocol, an agreement on how those programs will communicate. Before delving

into the design details of a protocol, high- level decisions must be made about which

program is expected to initiate communication and when responses are expected. For

example, a Web server is typically thought of as a long-running program (or daemon) that

sends network messages only in response to requests coming in from the network. The

other side of the protocol is a Web client, such as a browser, which always initiates

communication with the server. Clients normally communicate with one server at a time,

although using a Web browser as an example, we might communicate with many different

Web servers over, say, a 10-minute time period. But from the server's perspective, at any

given point in time, it is not unusual for a server to be communicating with multiple

clients.

Client –Server Computing:

Client Process:This is the process which typically makes a request for information. After

getting the response this process may terminate or may do some other processing.

For example: Internet Browser works as a client application which sends a request to Web

Server to get one HTML web page.

Server Process:This is the process which takes a request from the clients. After getting a

request from the client, this process will do required processing and will gather requested

information and will send it to the requestor client. Once done, it becomes ready to serve

another client. Server process are always alert and ready to serve incoming requests.

For example: Web Server keeps waiting for requests from Internet Browsers and as soon

as it gets any request from a browser, it picks up a requested HTML page and sends it

back to that Browser.

2-tier and 3-tier architectures:

There are two types of client server architectures:

2-tier architectures: In this architecture, client directly interact with the server. This

type of architecture may have some security holes and performance problems.

Internet Explorer and Web Server works on two tier architecture. Here security

problems are resolved using Secure Socket Layer(SSL).

3-tier architectures: In this architecture, one more software sits in between client

and server. This middle software is called middleware. Middleware are used to

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perform all the security checks and load balancing in case of heavy load. A

middleware takes all requests from the client and after doing required

authentication it passes that request to the server. Then server does required

processing and sends response back to the middleware and finally middleware

passes this response back to the client. If you want to implement a 3-tier

architecture then you can keep any middle ware like Web Logic or WebSphere

software in between your Web Server and Web Browsers.

Types of Server:

There are two types of servers you can have:

Iterative Server: This is the simplest form of server where a server process serves

one client and after completing first request then it takes request from another

client. Meanwhile another client keeps waiting.

Concurrent Servers: This type of server runs multiple concurrent processes to serve

many request at a time. Because one process may take longer and another client

can not wait for so long. The simplest way to write a concurrent server under Unix

is to fork a child process to handle each client separately.

How to make client:

The system calls for establishing a connection are somewhat different for the client and

the server, but both involve the basic construct of a socket. The two processes each

establish their own sockets.

The steps involved in establishing a socket on the client side are as follows:

1. Create a socket with the socket() system call.

2. Connect the socket to the address of the server using the connect() system call.

3. Send and receive data. There are a number of ways to do this, but the simplest is to

use the read() and write() system calls.

How to make a server:

The steps involved in establishing a socket on the server side are as follows:


2. Bind the socket to an address using the bind() system call. For a server socket on

the Internet, an address consists of a port number on the host machine.

3. Listen for connections with the listen() system call.

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4. Accept a connection with the accept() system call. This call typically blocks until a

client connects with the server.

5. Send and receive data using the read() and write() system calls.

Client and Server Interaction:

Following is the diagram showing complete Client and Server interaction:

What is socket?

Sockets allow communication between two different processes on the same or different

machines. To be more precise, it's a way to talk to other computers using standard Unix

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file descriptors. In Unix, every I/O actions are done by writing or reading to a file

descriptor. A file descriptor is just an integer associated with an open file and it can be a

network connection, a text file, a terminal, or something else.

Where socket is used?

A Unix Socket is used in a client server application frameworks. A server is a process

which does some function on request from a client. Most of the application level protocols

like FTP, SMTP and POP3 make use of Sockets to establish connection between client

and server and then for exchanging data.

Socket Types:

There are four types of sockets available to the users. The first two are most commenly

used and last two are rarely used.

Stream Sockets: Delivery in a networked environment is guaranteed. If you send

through the stream socket three items "A,B,C", they will arrive in the same order -

"A,B,C". These sockets use TCP (Transmission Control Protocol) for data

transmission. If delivery is impossible, the sender receives an error indicator. Data

records do no have any boundaries.

Datagram Sockets: Delivery in a networked environment is not guaranteed.

They're connectionless because you don't need to have an open connection as in

Stream Sockets - you build a packet with the destination information and send it

out. They use UDP (User Datagram Protocol).

Raw Sockets: provides users access to the underlying communication protocols

which support socket abstractions. These sockets are normally datagram oriented,

though their exact characteristics are dependent on the interface provided by the

protocol. Raw sockets are not intended for the general user; they have been

provided mainly for those interested in developing new communication protocols,

or for gaining access to some of the more esoteric facilities of an existing protocol.

Sequenced Packet Sockets: They are similar to a stream socket, with the exception

that record boundaries are preserved. This interface is provided only as part of the

Network Systems (NS) socket abstraction, and is very important in most serious

NS applications. Sequenced-packet sockets allow the user to manipulate the

Sequence Packet Protocol (SPP) or Internet Datagram Protocol (IDP) headers on a

packet or a group of packets either by writing a prototype header along with

whatever data is to be sent.

Network Addresses - IP Addresses:

The IP host address, or more commonly just IP address, is used to identify hosts connected

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to the Internet. IP stands for Internet Protocol and refers to the Internet Layer of the overall

network architecture of the Internet.

An IP address is a 32-bit quantity interpreted as 4 8-bit numbers or octets. Each IP address

uniquely identifies the participating user network, the host on the network, and the class of

the user network.

An IP address is usually written in a dotted-decimal notation of the form N1.N2.N3.N4,

where each Ni is a decimal number between 0 and 255 decimal (00 through FF

hexadecimal).

Address Classes:

IP addresses are managed and created by the Internet Assigned Numbers Authority

(IANA). There are 5 different address classes. You can determine which class any IP

address is in by examining the first 4 bits of the IP address.

Class A addresses begin with 0xxx, or 1 to 126 decimal.

Class B addresses begin with 10xx, or 128 to 191 decimal.

Class C addresses begin with 110x, or 192 to 223 decimal.

Class D addresses begin with 1110, or 224 to 239 decimal.

Class E addresses begin with 1111, or 240 to 254 decimal.

Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for

internal testing on a local machine; [ You can test this: you should always be able to ping

127.0.0.1, which points to yourself ] Class D addresses are reserved for multicasting;

Class E addresses are reserved for future use. They should not be used for host addresses.

Ports and Services:

When a client process wants to connect a server, the client must have a way of identifying

the server that it wants to connect. SO if the client knows the 32-bit Internet address of the

host on which the server resides it can contact that host. But how does the client identify

the particular server process running on that host ?

To resolve the problem of identifying a particular server process running on a host, both

TCP and UDP have defined a group of well known ports.

For our purposes, a port will be defined as an integer number between 1024 and 65535.

This is because all port numbers smaller than 1024 are considered well-known -- for

example, telnet uses port 23, http uses 80, ftp uses 21, and so on.

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The port assignments to network services can be found in the file /etc/services. If you are

writing your own server then care must be taken to assign a port to your server. You

should make sure that this port should already be not assigned to any other server.

Port and Service Functions:

Unix provides following functions to fetch service name from the /etc/services file.

structservent *getservbyname(char *name, char *proto): - This call takes service

name and protocol name and returns corresponding port number for that service.

structservent *getservbyport(int port, char *proto): - This call takes port number

and protocol name and returns corresponding service name.

The return value for each function is a pointer to a structure with the following form:

structservent

{

char *s_name;

char **s_aliases;

ints_port;

char *s_proto;

};

Here is the description of the member fields:

Attribute Values Description

s_name http This is official name of the service. For example SMTP, FTP POP3

etc.

s_aliases ALIAS This will hold list of service aliases. Most of the time this will be

set to NULL.

s_port 80 This will have associated port number. For example for HTTP this

will be 80.

s_proto TCP

UDP

This will be set to the protocol used. Internet services are provided

using either TCP or UDP.

Byte Ordering Functions:

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unsignedshort htons(unsigned short hostshort)

This function converts 16-bit (2-byte) quantities from host byte order to network byte

order.

unsigned long htonl(unsigned long hostlong)

This function converts 32-bit (4-byte) quantities from host byte order to network byte

order.

unsigned short ntohs(unsigned short netshort)

This function converts 16-bit (2-byte) quantities from network byte order to host byte

order.

unsigned long ntohl(unsigned long netlong)

This function converts 32-bit quantities from network byte order to host byte order.

IP Address Functions:

UNIX provides various function calls that will help you manipulating IP addresses. These

functions convert Internet addresses between ASCII strings (what humans prefer to use)

and network byte ordered binary values (values that are stored in socket address

structures).

There are following three function calls which are used for IPv4 addressing:

intinet_aton(const char *strptr, structin_addr *addrptr):

This function call converts the specified string, in the Internet standard dot notation, to

a network address, and stores the address in the structure provided. The converted

address will be in Network Byte Order (bytes ordered from left to right). This returns 1

if string was valid and 0 on error.

in_addr_tinet_addr(const char *strptr):

This function call converts the specified string, in the Internet standard dot notation, to

an integer value suitable for use as an Internet address. The converted address will be

in Network Byte Order (bytes ordered from left to right). This returns a 32-bit binary

network byte ordered IPv4 address and INADDR_NONE on error.

char *inet_ntoa(structin_addrinaddr):

This function call converts the specified Internet host address to a string in the Internet

standard dot notation.

Socket Core Functions:

This tutorial describes the core socket functions required to write a complete TCP client

and server.

The socket Function:

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To perform network I/O, the first thing a process must do is call the socket function,

specifying the type of communication protocol desired and protocol family etc.

#include <sys/types.h>

#include <sys/socket.h>

int socket (int family, int type, int protocol);

This call gives you a socket descriptor that you can use in later system calls or it gives you

-1 on error.

Parameters:

family: specifies the protocol family and is one of the constants shown below:

Family Description

AF_INET IPv4 protocols

AF_INET6 IPv6 protocols

AF_LOCAL Unix domain protocols

AF_ROUTE Routing Sockets

AF_KEY Ket socket

The connect Function:

The connect function is used by a TCP client to establish a connection with a TCP server.



int connect(intsockfd, structsockaddr *serv_addr, intaddrlen);

This call returns 0 if it successfully connects to the server otherwise it gives you -1 on

error.

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Parameters:

sockfd: is a socket descriptor returned by the socket function.

serv_addr is a pointer to structsockaddr that contains destination IP address and

port.

addrlen set it to sizeof(structsockaddr).

The bind Function:

The bind function assigns a local protocol address to a socket. With the Internet protocols,

the protocol address is the combination of either a 32-bit IPv4 address or a 128-bit IPv6

address, along with a 16-bit TCP or UDP port number. This function is called by TCP

server only.



int bind(intsockfd, structsockaddr *my_addr,intaddrlen);

This call returns 0 if it successfully binds to the address otherwise it gives you -1 on error.

Parameters:


my_addr is a pointer to structsockaddr that contains local IP address and port.


The listen Function:

The listen function is called only by a TCP server and it performs two actions:

The listen function converts an unconnected socket into a passive socket,

indicating that the kernel should accept incoming connection requests directed to

this socket.

The second argument to this function specifies the maximum number of

connections the kernel should queue for this socket.



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int listen(intsockfd,int backlog);

This call returns 0 on success otherwise it gives you -1 on error.

Parameters:


backlog is the number of allowed connections.

The accept Function:

The accept function is called by a TCP server to return the next completed connection

from the front of the completed connection queue. If the completed connection queue is

empty, the process is put to sleep.

The listen function converts an unconnected socket into a passive socket,

indicating that the kernel should accept incoming connection requests directed to

this socket.

The second argument to this function specifies the maximum number of

connections the kernel should queue for this socket.



int accept (intsockfd, structsockaddr *cliaddr, socklen_t *addrlen);

This call returns non negative descriptor on success otherwise it gives you -1 on error. The

returned decriptor is assumed to be a client socket descriptor and all read write operations

will be done on this descripton to communicate with the client.

Parameters:


cliaddr is a pointer to structsockaddr that contains client IP address and port.


The send Function:

The send function is used to send data over stream sockets or CONNECTED datagram

sockets. If you want to send data over UNCONNECTED datagram sockets you must use

sendto() function.

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You can use write() system call to send the data. This call is explained in helper functions

tutorial.

int send(intsockfd, const void *msg, intlen, int flags);

This call returns the number of bytes sent out otherwise it will return -1 on error.

Parameters:


msg is a pointer to the data you want to send.

len is the length of the data you want to send (in bytes).

flags is set to 0.

The recv Function:

The recv function is used to receive data over stream sockets or CONNECTED datagram

sockets. If you want to receive data over UNCONNECTED datagram sockets you must

use recvfrom().

You can use read() system call to read the data. This call is explained in helper functions

tutorial.

intrecv(intsockfd, void *buf, intlen, unsigned int flags);

This call returns the number of bytes read into the buffer otherwise it will return -1 on

error.

Parameters:


buf is the buffer to read the information into.

len is the maximum length of the buffer.

flags is set to 0.

The sendto Function:

The sendto function is used to send data over UNCONNECTED datagram sockets. Put

simply, when you use scoket type as SOCK_DGRAM

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intsendto(intsockfd, const void *msg, intlen, unsigned int flags,

conststructsockaddr *to, inttolen);

This call returns the number of bytes sent otherwise it will return -1 on error.

Parameters:


msg is a pointer to the data you want to send.

len is the length of the data you want to send (in bytes).

flags is set to 0.

to is a pointer to structsockaddr for the host where data has to be sent.

tolen is set it to sizeof(structsockaddr).

The recvfrom Function:

The recvfrom function is used to receive data from UNCONNECTED datagram sockets.

Put simply, when you use scoket type as SOCK_DGRAM

intrecvfrom(intsockfd, void *buf, intlen, unsigned int flags

structsockaddr *from, int *fromlen);

This call returns the number of bytes read into the buffer otherwise it will return -1 on

error.

Parameters:


buf is the buffer to read the information into.

len is the maximum length of the buffer.

flags is set to 0.

from is a pointer to structsockaddr for the host where data has to be read.

fromlen is set it to sizeof(structsockaddr).

The close Function:

The close function is used to close the communication between client and server.

int close( intsockfd );

This call returns 0 on success otherwise it will return -1 on error.

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Parameters:


The shutdown Function:

The shutdown function is used to gracefully close the communication between client and

server. This function gives more control in caomparision of close function.

int shutdown(intsockfd, int how);

This call returns 0 on success otherwise it will return -1 on error.

Parameters:


how: put one of the numbers:

o 0 indicates receives disallowed,

o 1indicatesthat sends disallowed and

o 2indicates that sends and receives disallowed. When how is set to 2, it's the

same thing as close().

The select Function:

The select function indicates which of the specified file descriptors is ready for reading,

ready for writing, or has an error condition pending.

Socket Helper Functions:

This tutorial describes all the helper functions which are used while doing socket

programming. Other helper functions are described in Ports and Services, Netowrk Byte

Orders tutorials.

The write Function:

The write function attempts to write nbyte bytes from the buffer pointed to by buf to the

file associated with the open file descriptor, fildes.

You can also use send() function to send data to another process.

#include <unistd.h>

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int write(intfildes, const void *buf, intnbyte);

Upon successful completion, write() returns the number of bytes actually written to the file

associated with fildes. This number is never greater than nbyte. Otherwise, -1 is returned,

Parameters:

fildes: is a socket descriptor returned by the socket function.

buf is a pointer to the data you want to send.

nbyte is the number of bytes to be written. If nbyte is 0, write() will return 0 and

have no other results if the file is a regular file; otherwise, the results are

unspecified.

The read Function:

The read function attempts to read nbyte bytes from the file associated with the open file

descriptor, fildes, into the buffer pointed to by buf.

You can also use recv() function to read data to another process.

#include <unistd.h>

int read(intfildes, const void *buf, intnbyte);

Upon successful completion, write() returns the number of bytes actually written to the file

associated with fildes. This number is never greater than nbyte. Otherwise, -1 is returned,

Parameters:

fildes: is a socket descriptor returned by the socket function.

buf is the buffer to read the information into..

nbyte is the number of bytes to read.

The fork Function:

The forkfunction create a new process. The new process is called child process will be an

exact copy of the calling process (parent process). The child process inherits many

attributes from the parent process.


#include <unistd.h>

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int fork(void);

Upon successful completion, fork() return 0 to the child process and return the process ID

of the child process to the parent process. Otherwise -1 is returned to the parent process,

no child process is created and errno is set to indicate the error.

Parameters:

void: means no parameter is required.

The bzero Function:

The bzero function places nbyte null bytes in the string s. This function will be used to set

all the socket structures with null values.

void bzero(void *s, intnbyte);

This function does not return anything.

Parameters:

s: specifies string which has to be filled with null bytes.This will be a point to

socket structure variable

nbyte: specifies the number of bytes to be filled with null values. This will be the

size of the socket structure.

The bcmp Function:

The bcmp function compares byte string s1 against byte string s2. Both strings are

assumed to be nbyte bytes long.

intbcmp(const void *s1, const void *s2, intnbyte);

This function returns 0 if both strings are identical, 1 otherwise. The bcmp() function

always returns 0 when nbyte is 0.

Parameters:

s1: specifies the first string to be compared.

s2: specifies the second string to be compared.

nbyte: specifies the number of bytes to be compared.

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The bcopy Function:

The bcopy function copies nbyte bytes from string s1 to the string s2. Overlapping strings

are handled correctly.

void bcopy(const void *s1, void *s2, intnbyte);

This function does not return anything.

Parameters:

s1: specifies the source string.

s2: specifies the destination string.

nbyte: specifies the number of bytes to be copied.

The memset Function:

The memset function is also used to set structure variables in the same way as bzero.

void *memset(void *s, int c, intnbyte);

This function returns a pointer to void, in fact pointer to the set memory and you need to

caste it accordingly.

Parameters:

s: specifies the source to be set.

c: specifies the character to set on nbyte places..

nbyte: specifies the number of bytes to be set

Socket Server Function:

We have seen in one of the tutorials that to make a process a TCP server following steps

are required:


2. Bind the socket to an address using the bind() system call. For a server socket on

the Internet, an address consists of a port number on the host machine.

3. Listen for connections with the listen() system call.

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4. Accept a connection with the accept() system call. This call typically blocks until a

client connects with the server.

5. Send and receive data using the read() and write() system calls.

Handle Multiple Connections:

To allow the server to handle multiple simultaneous connections, we make the following

changes in the above code:

1. Put the accept statement and the following code in an infinite loop.

2. After a connection is established, call fork() to create a new process.

3. The child process will close sockfd and call doprocessing function, passing the

new socket file descriptor as an argument. When the two processes have completed

their conversation, as indicated by doprocessing() returning, this process simply

exits.

4. The parent process closes newsockfd. Because all of this code is in an infinite loop,

it will return to the accept statement to wait for the next connection.

Socket client function:

We have seen in one of the tutorials that to make a process a TCP client following steps

are required:


2. Connect the socket to the address of the server using the connect() system call.

3. Send and receive data. There are a number of ways to do this, but the simplest is to

use the read() and write() system calls.

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TCP/IP Model vs. OSI Model

TCP/IP model and the OSI model have been the two protocol suites on which the

communication industry heavily relies on. Both TCP/IP model and OSI model work in a

very similar fashion. But they do have very subtle differences too. Knowing these

differences is very crucial to learning computer networking.

A Background:

OSI reference model came into existence way before the TCP/IP model was created.

Advance research project agency (ARPA) created a (Department of Defence) DOD

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reference model so that they could logically group the similarly working components of

the network into various layers of the protocol.

Established in 1947, the International Standards Organization (ISO) is a multinational

body dedicated to worldwide agreement on international standards. An ISO standard that

covers all aspects of network communications is the Open Systems Interconnection (OSI)

model. It was first introduced in the late 1970s.

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TCP/IP Model Layers Explained:

It is a suite of protocol which is named after its most significant pair of protocols. That is

Transmission Control Protocol and Internet Protocol. TCP/IP are made up of layers. Each

layer is responsible for a set of computer network related tasks. Every layer provides service

to the layer above it. In all, there are four layers in the TCP/IP reference model.

Application Layer: This is the topmost layer of the TCP/IP suite. The three topmost

layers in the OSI model, however, are represented in TCP/IP by a single layer called

the application layer. This is responsible for coding of the packet data.

Transport Layer: This layer monitors end-to-end path selections of the packets. It

also provides service to the application layer.

Internet Layer: This layer is responsible for sending packets through different

networks.

Link Layer: Last two layers in the OSI model, however, are represented in TCP/IP by

a single layer called the link layer. It is the closest layer to the network hardware. It

provides service to Internet layer.

OSI Model Layers Explained:

In OSI reference model there seven layers of protocols. Again, in OSI reference model, each

layer provides services to the layer above it. These are all seven layers of OSI model.

Physical Layer: It is the lower most layer of the OSI reference model. It is layer

which is responsible for direct interaction of the OSI model with hardware. The

hardware provides service to the physical layer and it provides service to the data link

layer.

Data Link Layer: There may be certain errors which may occur at the physical layer.

If possible, these errors are corrected by the data link layer. The data link layer

provides the way by which various entities can transfer the data to the network.

Network Layer: It does not allow the quality of the service to be degraded that was

requested by the transport layer. It is also responsible for data transfer sequence from

source to destination.

Transport Layer: The reliability of the data is ensured by the transport layer. It also

retransmits those data that fail to reach the destination.

Session Layer: The session layer is responsible for creating and terminating the

connection. Management of such a connection is taken care of by the session layer.

Presentation Layer: This layer is responsible for decoding the context (syntax and

semantics) of the higher level entities.

Application Layer: Whichever software application that implements socket

programming will communicate with this layer. This layer is closest to the user.

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TCP/IP Model vs. OSI Model:

The entire communication industry stands on the backbone of TCP/IP and OSI reference

model. It is very vital to learn the above differences, if anyone wants to be an expert in the

field of communication.

Sr.

No. TCP/IP Reference Model OSI Reference Model

1 Defined after the advent of Internet Defined before advent of internet

2 Service interface and protocols were not clearly

distinguished before

Service interface and protocols are

clearly distinguished

3 TCP/IP supports Internet working Internet working not supported

4 Loosely layered Strict layering

5 Protocol Dependent standard Protocol independent standard

6 More Credible Less Credible

7 TCP reliably delivers packets, IP does not

reliably deliver packets All packets are reliably delivered

Difference between TCP and UDP:

Both TCP and UDP work at transport layer TCP/IP model, but have very different usage. The

most important differences are explained below.

Reliability:

TCP: connection-oriented

UDP: connectionless

Ordered:

TCP: order of message receipt is guaranteed

UDP: order is not guaranteed

Protocol we ight:

TCP: heavyweight, because of the connection/ordering overhead

UDP: lightweight, very few overhead

Protocol used:

TCP: Typical protocols which use TCP are HTTP, FTP and SMTP

UDP: Examples of protocols using UDP are DNS and DHCP

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Packets:

TCP: streaming, data is read as a "stream," with nothing distinguishing where one

packet ends and another begins. There may be multiple packets per read call.

UDP: datagram, one packet per one read call.

Frame Structure of TCP & UDP:

When data is sent over the network, it needs to be encapsulated into so called "frames". There

are various methods of encapsulation depending on the protocol and topology that are being

used.

This is the TCP frame structure:

This is the UDP frame structure:

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LAB SESSION: 2

Network Theory

(1) PING: The ping command sends echo requests to the host you specify on the command

line, and lists the responses received their round trip time. Simply use ping as:

$ pingip_address or host_name

64 bytes from 8.3.1.5: icmp_seq=0 ttl=64 time=0.120 ms

64 bytes from 8.3.1.5: icmp_seq=1 ttl=64 time=0.050 ms

--- 8.3.1.5 ping statistics ---

2 packets transmitted, 2 received, 0% packet loss, time 1000ms

To stop ping use CTRL-C (break). ping command has various options :

1) -i interval

$ping ipaddress - i 60

Here interval 60 specifies that, send one ICMP packet every 60 seconds.

2) -c count

$ping ipaddress -c 3

The command will be terminated automatically after sending three ICMP packets to the

requested host. It stops after sending 3 ECHO_REQUEST packets.

3) -s packetsize

Specifies the number of data bytes to be sent. The default is 56, which translates into 64

ICMP data bytes when combined with the 8 bytes of ICMP header data.

(2) IFCONFIG: This command is used to configure network interfaces, or to display their

current configuration. If no arguments are given, ifconfig displays the status of the currently

active interfaces. If a single interface argument is given, it displays the status of the given

interface only; if a single -a argument is given, it displays the status of all interfaces, even

those that are down. We can use this command to activate and deactivate interfaces with the

"up" and "down" settings. Examples:

$ ifconfig //Displays information of all currently active interfaces

$ ifconfig eth0 //Displays information of interface eth0 (Ethernet 0) only

$ ifconfig -a //Displays information of all active as well as inactive interfaces

Usually ifconfig lists following information about the interface.

Interfaces that is currently up.

Ethernet hardware address as well as inet (IP) address of the interface.

Maximum Transmission Unit(MTU)

Number of packets transmitted on the interface and number of packets received on the

interface with all statistics.

(3) TELNET: Telnet is a TCP/IP application that provides remote terminal services. Telnet

allow a user from his or her network workstation to log in to a remote network station across

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the network and act as if the terminal station directly connected. The user starts the TELNET

protocol at the terminal by typing telnet <domain name or IP address>

$telnet 8.6.2.1 OR

$telnet ninad

The Telnet application would start and attempt to establish a connection to the remote device.

If an argument was not supplied, TELNET would wait for the user to OPEN a connection

using the DNS or IP address.

(4) NETSTAT: Print network connections, routing tables, interface statistics and multicast

memberships. By default, netstat displays a list of open sockets. If you don’t specify any

address families, then the active sockets of all configured address families will be printed.

Various options can be used with netstatare :

1) -r

$netstat -r //shows kernel IP routing table.

2) -i //provides information on the interface.

3) -t //Displays information of all TCP sockets

4) -u //Displays the information of all UDP sockets

5) –x //Displays the information of all UNIX internal sockets.

6) -a //Your default netstat command does not display sockets that are in

LISTENING mode. Use switch - a to display both listening and non-listening sockets.

(5) TRACEROUTE: traceroute will actually show the route. It attempts to list the series of

hosts through which your packets travel on their way to a given destination. It traces path to

destination discovering MTU (Maximum Transmission Unit) along this path.

$ tracepath 8.6.1.20

(6) RLOGIN: Stand for remote login. Rlogin command logs into a specified remote host and

connects your local terminal to the remote host. Examples:

To log in to a remote host with your local user name, enter:

$rlogin host2

You are prompted to enter your password and then are logged in to the remote host host2. To

logoff the remote host, and close the connection, enter ~. (tilde, period).

To log into a remote host with a different user name, enter;

$ rlogin host2 - l dale

You are prompted to enter your password and then are logged in to the remote host host2 with

the user name dale. To logoff the remote host, and close the connection, enter ~. (tilde,

period).

UNP Lab

LAB SESSION: 3

Objective: Write a Program to Find out the Host Name and IP address of Host using

Unix networking programming.

Host Name And IP

Host.c

# include <stdio.h>

# include <netdb.h>

# include <netinet/in.h>

# include <arpa/inet.h>

int main()

{

char hostname[1024];

char *inputbuf;

hostname[1023]='\0';

gethostname(hostname,1023);

printf("Hostname:%s \n ", hostname);

structhostent *h;

h=gethostbyname(hostname);

inputbuf=inet_ntoa(*((structin_addr *)h->h_addr_list[1]));

printf("h_name: %s IP : %s", h->h_name, inputbuf);

return 0;

}

UNP Lab

UNP Lab

LAB SESSION: 4

Client Server Communication

Objective: Write a Program to demonstrate the client and server communication using

Unix Socket programming.

Client.c

#include<sys/socket.h>

#include<sys/types.h>

#include<arpa/inet.h>

#include<stdio.h>

#include<netinet/in.h>

#define ser_ip "127.0.0.1"

#define port 3253

int main()

{

structsockaddr_incin;

intclts,cltlen;

clts=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);

cin.sin_family=AF_INET;

cin.sin_port=htons(port);

cin.sin_addr.s_addr=inet_addr(ser_ip);

cltlen=sizeof(cin);

if(connect(clts,(structsockaddr*)&cin,cltlen)>=0)

printf("Server connected");

else

printf("Server not connected");

return 0;

}

UNP Lab

Server.c




#include<stdio.h>



#define port 3253

int main()

{

structsockaddr_incin,sin;

intsers,serlen,clts,cltlen;

sers=socket(AF_INET,SOCK_STREAM,0);

sin.sin_family=AF_INET;

sin.sin_port=htons(port);

sin.sin_addr.s_addr=inet_addr(ser_ip);

serlen=sizeof(sin);

cltlen=sizeof(cin);

if(bind (sers, (structsockaddr *) &sin, serlen) < 0)

{

perror("Not Binded:\n");

}

else

printf("Binded and Wait for client...\n");

listen (sers,1 );

clts = accept (sers, (structsockaddr *) &cin, &cltlen);

if(clts>=0)

printf("Server connected");

else


return 0;

}

UNP Lab

UNP Lab

LAB SESSION: 5

Client Server Messaging

Objective: Write a Program to demonstrate the client and server communication using

Unix Socket programming.

Sermsg.c




#include<stdio.h>


#include<stdlib.h>

#include<string.h>

#include<unistd.h>


#define port 3253

int main()

{


intsers,serlen,clts,cltlen,n;

char msg1[100],msg2[100];





serlen=sizeof(sin);

cltlen=sizeof(cin);


{


}

else


listen (sers,1 );


if(clts>=0)

{

do

{

fflush(stdin);

UNP Lab

n=read(clts,msg1,100);

msg1[n]='\0';

printf("Client: %s\n",msg1);

fflush(stdin);

printf("Server: ");

gets(msg2);

printf("\n");

write(clts,msg2,100);

}while((strcmp(msg2,"exit")!=0)&&(strcmp(msg2,"exit")!=0));

exit(1);

}

else


return 0;

}

Clientmsg.c




#include<stdio.h>


#include<stdlib.h>

#include<string.h>

#include<unistd.h>


#define port 3253

int main()

{


intsers,serlen,clts,cltlen,n;

char msg1[100],msg2[100];





serlen=sizeof(sin);

cltlen=sizeof(cin);


{

UNP Lab


}

else


listen (sers,1 );


if(clts>=0)

{

do

{

fflush(stdin);

n=read(clts,msg1,100);

msg1[n]='\0';

printf("Client: %s\n",msg1);

fflush(stdin);

printf("Server: ");

gets(msg2);

printf("\n");

write(clts,msg2,100);

}while((strcmp(msg2,"exit")!=0)&&(strcmp(msg2,"exit")!=0));

exit(1);

}

else


return 0;

}

UNP Lab

unix network lab manual

Documents

maximum transmission unit

const char strptr

const void s1

helper functions tutorial

call typically blocks

osi reference model

socket descriptor returned

network byte order