DOMAIN NAME SYSTEM

AIM:
           To write a program to display the host address for the given domain name.

ALGORITHM:
SERVER:

    STEP 1: Start
    STEP 2: Declare the variables for the socket
    STEP 3: Specify the family, protocol, IP address and port number
    STEP 4: Create a socket using socket() function
    STEP 5: Bind the IP address and Port number
    STEP 6: Listen and accept the client’s request for the connection
    STEP 7: Read the domain name and display if it is binded
    STEP 8: Display the error message if it is not binded
    STEP 9: Stop
CLIENT:
    STEP 1: Start
    STEP 2: Declare the variables for the socket
    STEP 3:  Specify the family, protocol, IP address and port number
    STEP 4: Create a socket using socket() function
    STEP 5: Check whether the connection is established or not
    STEP 6: Get the domain name
    STEP 7: Display the corresponding IP address for the domain name
    STEP 8: Stop

SOURCE CODE:
SERVER:

#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<stdio.h>
#include<stdlib.h>
#include<netdb.h>
#define SA struct sockaddr
int main()
{
        int listenfd,connfd;
        socklen_t len;
        struct sockaddr_in servaddr,cliaddr;
        struct hostent*hp,tp;
        char host[50],buff[100];
        listenfd=socket(AF_INET,SOCK_STREAM,0);
        bzero(&servaddr,sizeof(servaddr));
        servaddr.sin_family=AF_INET;
        servaddr.sin_port=htons(5035);
        servaddr.sin_addr.s_addr=htons(INADDR_ANY);
        printf("\nBinded");
        bind(listenfd,(SA*)&servaddr,sizeof(servaddr));
        listen(listenfd,10);
        for(;;)
        {
                len=sizeof(cliaddr);
                connfd=accept(listenfd,(SA*)&cliaddr,&len);
                read(connfd,host,sizeof(host));
                printf("\n\t%s",host);
                 if((hp=gethostbyname(host))==NULL)
                    printf("\nCan't get address");
                 if(inet_ntop(AF_INET,hp->h_addr,buff,sizeof(buff))<=0)
                    printf("\nHost address is not available");
                printf("\n\t%s",buff);
                write(connfd,buff,strlen(buff)+1);
                close(connfd);
        }
        return 0;
}

CLIENT:
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<stdio.h>
#include<netdb.h>
#include<stdlib.h>
#define SA struct sockaddr
int main(int argc,char **argv)
{
        socklen_t len;
        struct sockaddr_in servaddr;
        struct hostent tp;
        char buff[100],host[50];
        int sockfd;
        sockfd=socket(AF_INET,SOCK_STREAM,0);
        bzero(&servaddr,sizeof(servaddr));
        servaddr.sin_family=AF_INET;
        servaddr.sin_port=htons(5035);
        servaddr.sin_addr.s_addr=inet_addr("127.0.0.1");
         if(connect(sockfd,(SA*)&servaddr,sizeof(servaddr))<0)
            printf("Connect Error");
        printf("\nEnter the Domain Name : ");
        scanf("%s",host);
        write(sockfd,host,strlen(host)+1);
         if(read(sockfd,buff,sizeof(buff))<0)
            printf("\nRead Error");
        printf("\nThe host address : %s\n",buff);
        return 0;
}

OUTPUT:
SERVER:


















CLIENT:


















RESULT:
    Thus the program for Domain Name System was executed and the output was
verified.
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