Implementation UDP Sockets

What is Sockets?

Sockets are the endpoints of a bidirectional communications channel. Sockets may communicate within a process, between processes on the same machine, or between processes on different continents.

Sockets may be implemented over a number of different channel types: Unix domain sockets, TCP, UDP, and so on. The socket library provides specific classes for handling the common transports as well as a generic interface for handling the rest. Sockets have their own vocabulary −Sr.No. Term & Description

Domain

The family of protocols that is used as the transport mechanism. These values are constants such as AF_INET, PF_INET, PF_UNIX, PF_X25, and so on.

type

The type of communications between the two endpoints, typically SOCK_STREAM for connection-oriented protocols and SOCK_DGRAM for connectionless protocols.

protocol

Typically zero, this may be used to identify a variant of a protocol within a domain and type.

hostname

The identifier of a network interface −

 A string, which can be a host name, a dotted-quad address, or an

IPV6 address in colon (and possibly dot) notation

 A string "<broadcast>", which specifies an INADDR_BROADCAST

address.

 A zero-length string, which specifies INADDR_ANY, or

 An Integer, interpreted as a binary address in host byte order.

5

port

Each server listens for clients calling on one or more ports. A port may be a Fixnum port number, a string containing a port number, or the name of a service.

A Simple Server

To write Internet servers, we use the socket function available in socket  module to create a socket object. A socket object is then used to call other functions to setup a socket server.

A Simple Client

Let us write a very simple client program which opens a connection to a given port 12345 and given host. This is very simple to create a socket client using Python's socket module function.

Udp server.py

import socket

UDP_IP = "127.0.0.1"

UDP_PORT = 5005

sock = socket.socket(socket.AF_INET, # Internet

                     socket.SOCK_DGRAM) # UDP

sock.bind((UDP_IP, UDP_PORT))

while True:

    data, addr = sock.recvfrom(1024) # buffer size is 1024 bytes

    print ("received message:", data,"from", addr)

Udp Client.py

import socket

UDP_IP = "127.0.0.1"

UDP_PORT = 5005

MESSAGE = "Hello, World!"

sock = socket.socket(socket.AF_INET, # Internet

                     socket.SOCK_DGRAM) # UDP

sock.bind(('', 54312))

sock.sendto(MESSAGE.encode('ascii'), (UDP_IP, UDP_PORT))

Output:

UDP server up and listening

Message from Client:b"Hello UDP Server"

Client IP Address:("127.0.0.1", 51696)

Message from Server b"Hello UDP Client"

Implementation of Tcp socket

Client Side Programming

Establish a Socket Connection

To connect to other machine we need a socket connection. A socket connection means the two machines have information about each other’s network location (IP Address) and TCP port.The java.net.Socket class represents a Socket. To open a socket:

Socket socket = new Socket(“127.0.0.1”, 5000)

·         First argument – IP address of Server. ( 127.0.0.1  is the IP address of localhost, where code will run on single stand-alone machine).

·         Second argument – TCP Port. (Just a number representing which application to run on a server. For example, HTTP runs on port 80. Port number can be from 0 to 65535)

To communicate over a socket connection, streams are used to both input and output the data.

Closing the connection

The socket connection is closed explicitly once the message to server is sent.

In the program, Client keeps reading input from user and sends to the server until “Over” is typed.

Java Implementation

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// A Java program for a Client import java.net.*; import java.io.*;    public class Client {     // initialize socket and input output streams     private Socket socket            = null;     private DataInputStream  input   = null;     private DataOutputStream out     = null;        // constructor to put ip address and port     public Client(String address, int port)     {         // establish a connection         try         {             socket = new Socket(address, port);             System.out.println("Connected");                // takes input from terminal             input  = new DataInputStream(System.in);                // sends output to the socket             out    = new DataOutputStream(socket.getOutputStream());         }         catch(UnknownHostException u)         {             System.out.println(u);         }         catch(IOException i)         {             System.out.println(i);         }            // string to read message from input         String line = "";            // keep reading until "Over" is input         while (!line.equals("Over"))         {             try             {                 line = input.readLine();                 out.writeUTF(line);             }             catch(IOException i)             {                 System.out.println(i);             }         }            // close the connection         try         {             input.close();             out.close();             socket.close();         }         catch(IOException i)         {             System.out.println(i);         }     }        public static void main(String args[])     {         Client client = new Client("127.0.0.1", 5000);     } }

Server Programming

Establish a Socket Connection

To write a server application two sockets are needed.

·         A ServerSocket which waits for the client requests (when a client makes a new Socket())

·         A plain old Socket socket to use for communication with the client.

Communication

getOutputStream() method is used to send the output through the socket.

Close the Connection

After finishing,  it is important to close the connection by closing the socket as well as input/output streams.

// A Java program for a Server import java.net.*; import java.io.*;    public class Server {     //initialize socket and input stream     private Socket          socket   = null;     private ServerSocket    server   = null;     private DataInputStream in       =  null;        // constructor with port     public Server(int port)     {         // starts server and waits for a connection         try         {             server = new ServerSocket(port);             System.out.println("Server started");                System.out.println("Waiting for a client ...");                socket = server.accept();             System.out.println("Client accepted");                // takes input from the client socket             in = new DataInputStream(                 new BufferedInputStream(socket.getInputStream()));                String line = "";                // reads message from client until "Over" is sent             while (!line.equals("Over"))             {                 try                 {                     line = in.readUTF();                     System.out.println(line);                    }                 catch(IOException i)                 {                     System.out.println(i);                 }             }             System.out.println("Closing connection");                // close connection             socket.close();             in.close();         }         catch(IOException i)         {             System.out.println(i);         }     }        public static void main(String args[])     {         Server server = new Server(5000);     } }

1. First run the Server application as ,

$ java Server

Server started
Waiting for a client …

2. Then run the Client application on another terminal as,

$ java Client

It will show – Connected and the server accepts the client and shows,

Client accepted

3. Then you can start typing messages in the Client window. Here is a sample input to the Client

Hello

I made my first socket connection

Over

Which the Server simultaneously receives and shows,

Hello

I made my first socket connection

Over

Closing connection

Notice that sending “Over” closes the connection between the Client and the Server just like said before.

Rip configuration in cisco packet tracer

The Routing Information Protocol (RIP) sends routing-update messages at regular intervals and when the network topology changes. When a device receives a RIP routing update that includes changes to an entry, the deice updates its routing table to reflect the new route. After updating its routing table, the device immediately begins transmitting RIP routing updates to inform other network devices of the change.

Procedure:

• now drag and drop switches and pcs into the work space
• connect switches and pcs using copper straight wires in the fast Ethernet ports.
• provide pc with IP address and gateway to the pcs.

add IP address to the pc by double clicking on the pc and going to IP configuration mode.

• connect routers and switches using Gigabit port

Configuration of routers: Router 1:

Router(config-if)#exit

Router(config)#interface Serial0/1/1

Router(config-if)#ip address 10.10.10.20 255.0.0.0

Router(config-if)#ip address 10.10.10.20 255.0.0.0

Router(config-if)#no shutdown

Router(config-if)#

%LINK-5-CHANGED: Interface Serial0/1/1, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1/1, changed state to up.

similarly for router 2 has to be done.

CONFIGURATION OF RIP USING CLI IN CISCO PACKET TRACER:

·                                             after the implementation above routing config.go to CLI.

·                                             Type no ip route network_ip network_subnet gateway_router_address.

·                                             router rip and hit enter.

·                                             Type network address subnet etc

·                                             As shown below:

Similary for 2^nd router has to be done.

Result:

The RIP is configured.

Implementation of network address translation in cisco packet tracer

 Network address translation (NAT) is a method of remapping one IP address space into another by modifying network address information in the ip header of packets while they are in transit across a traffic routing device. The technique was originally used as a shortcut to avoid the need to readdress every host when a network was moved. It has become a popular and essential tool in conserving global address space in the face of IPv4 address exhaustion. One Internet-routable IP address of a NAT gateway can be used for an entire private network.

Fig1

Types of NAT:

Static NAT: In this, a single private IP address is mapped with single Public IP address, i.e., a private IP address is translated to a public IP address. It is used in Web hosting.

Dynamic NAT: In this type of NAT, multiple private IP address are mapped to a pool of public IP address. It is used when we know the number of fixed users wants to access the Internet at a given point of time.

Procedure:

1.      Drag and drop the network devices to create the above topology using interfaces.

2.      Assign IP Address to the devices as follows:

a.       PC0:  10.0.0.10

b.      PC1:   10.0.0.20

c.       PC3:   10.0.0.30

d.      ROUTER 0 SE 0/1/0 100.0.0.1

e.       ROUTER 0 GIG0/1   10.0.0.1

f.        ROUTER 1 SE0/1/0 100.0.0.2

g.      ROUTER 1 GIG0/1   192.168.1.1

h.      SERVER 0  192.168.1.10

3.      Assign network address to the Router in cli as follows:

·         Router 1:

Router#en

Router#config t

Router(config)#interface Gig0/0

Router(config-if)#ip address 10.0.0.1 255.0.0.0

Router(config-if)#no shutdown

Router(config-if)#exit

Router(config)#interface set0/1/0

Router(config-if)#ip address 100.0.0.2 255.0.0.0

Router(config-if)#no shutdown

Router(config-if)#exit

  

   Router 2:

Router#configure terminal

Router(config)#interface gig0/1

Router(config-if)#ip address 192.168.1.1 255.255.255.0

ROUTER(config-if)#no shutdown

ROUTER(config-if)#exit

ROUTER(config)#interface Set0/1/0

ROUTER(config-if)#ip address 100.0.0.2 255.0.0.0

ROUTER(config-if)#no shutdown

ROUTER(config-if)#exit

4. Configure Static NAT:

Static NAT configuration requires three steps: -

• Define IP address mapping
• Define inside local interface
• Define inside global interface
• Syntax:

Router(config)#ip nat inside source static [inside local ip address] [inside global IP address]

Router 1 NAT configuration:

Result:

Testing Static NAT Configuration:

Type following command in the command prompt.

Router#show ip nat translations

Pro Inside global Inside local Outside local Outside global

--- 50.0.0.10 10.0.0.10 --- ---

--- 50.0.0.20 10.0.0.20 --- ---

--- 50.0.0.30 10.0.0.30 --- ---

Implementation of DHCP in cisco packet tracer

Dynamic Host Configuration Protocol (DHCP) is an application layer protocol used to distribute various network configuration parameters to devices on a TCP/IP network. – IP addresses, subnet masks, default gateways, DNS servers, etc

Procedure:

1.      Create the above topology shown using the cisco packet tracer work space.

2.      Assign IP address to the gig interface as following:

3.      A Cisco router can be configured as a DHCP server. Here are the steps:

·         Exclude IP addresses from being assigned by DHCP by using the ip dhcp excluded-address FIRST_IP LAST_IP

·         Create a new DHCP pool with the ip dhcp pool NAME command.

·         Define a subnet that will be used to assign IP addresses to hosts with the network SUBNET SUBNET_MASK command.

·         Define the default gateway with the default-router IP command.

·         Define the DNS server with the dns-server IP address command.

·         (Optional) Define the DNS domain name by using the ip domain-name NAME command.

·         (Optional) Define the lease duration by using the lease DAYS HOURS MINUTES command. If you don’t specify this argument, the default lease time of 24 hours will be used.

 

Router(config-if)#ip dhcp pool IP01

Router(dhcp-config)#net 192.168.100.0 255.255.255.0

Router(dhcp-config)#exit

Router(config)#ip dhcp exec 192.168.100.1 192.168.100.15

^

% Invalid input detected at '^' marker.

Router(config)#ip dhcp exc 192.168.100.1 192.168.100.1

Router(config)#exit

Router#

%SYS-5-CONFIG_I: Configured from console by console

4.      Now click on the generic pc 0 , go to IP configuration and select DHCP.

 Result:

DHCP server has been implemented: