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yvrakeshyvrakesh
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April 14 Experiment 9 submission
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‎Sem-6/Networks Lab/Week-09/Assignment/Exp 9 DNS Server.pdf‎

60.9 KB
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‎Sem-6/Networks Lab/Week-09/Assignment/Exp9DNSServer_Revised.pdf‎

60.3 KB
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‎Sem-6/Networks Lab/Week-09/Assignment/dns_server.c‎

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#include<stdio.h>
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#include<stdlib.h>
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#include<string.h>
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#include<netinet/in.h>
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#include<sys/socket.h>
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#include<sys/types.h>
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#include<netdb.h>
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#include<arpa/inet.h>
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#include<unistd.h>
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#include<stdbool.h>
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#include<ctype.h>
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#define BUFF_LEN 4096
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#define MAX_SUB_DOMAIN 20
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#define SUB_DOMAIN_LEN 50
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#define MAX_NAME_SERVERS 20
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int parse(char *domain,char *name_server, char nameservers[][SUB_DOMAIN_LEN]){
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char command[BUFF_LEN];
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strcpy(command,"nslookup -type=ns ");
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strcat(command,domain);
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strcat(command," ");
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strcat(command,name_server);
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printf("%s\n",command);
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const char * cmd = command;
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char result[BUFF_LEN] = "";
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FILE * out = popen(cmd, "r");
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char buffer[BUFF_LEN];
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while (fgets (buffer, 1000, out))
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strcat(result,buffer);
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pclose(out);
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char *token;
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strtok(result,"\n");
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strtok(NULL,"\n");
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strtok(NULL,"\n");
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strtok(NULL,"=");
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token = strtok(NULL,"\n");
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int i = 0;
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while(token != NULL){
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strncpy(nameservers[i++],token+1,strlen(token)-2);
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strtok(NULL,"=");
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token = strtok(NULL,"\n");
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}
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return i;
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}
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int main(){
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int sockfd = socket(PF_INET,SOCK_DGRAM,0);
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if(sockfd == -1){
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printf("Failed to create a socket\n");
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return 0;
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}
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else if(sockfd <= 0){
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printf("Invalid memory creation for socket. Try again\n");
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return 0;
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}
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struct sockaddr_in serv_addr;
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serv_addr.sin_family = AF_INET;
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serv_addr.sin_port = htons(1234);
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serv_addr.sin_addr.s_addr = INADDR_ANY;
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memset(serv_addr.sin_zero,0,sizeof(serv_addr.sin_zero));
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int flag1 = bind(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr));
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if(flag1 == -1){
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printf("Failed to bind to an IP and port\n");
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close(sockfd);
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return 0;
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}
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struct sockaddr_storage serv_storage;
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int addr = sizeof(serv_storage);
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while(1){
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char buffer[BUFF_LEN];
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bzero(buffer,BUFF_LEN);
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while(1)
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if(recvfrom(sockfd,buffer,sizeof(buffer),0,(struct sockaddr *)&serv_storage,&addr) > 0)
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break;
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if(!strncmp(buffer,"quit",4)){
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printf("Requested to close the service\n");
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sendto(sockfd,buffer,strlen(buffer),0,(struct sockaddr *)&serv_storage,addr);
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break;
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}
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else{
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printf("Request from client is : %s",buffer);
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buffer[strlen(buffer)] = '\n';
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if(strncmp(buffer,"A ",2) && strncmp(buffer,"AAAA ",5) && strncmp(buffer,"NS ",3) && strncmp(buffer,"CNAME ",5)){
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char buff[] = "Illegal\n";
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sendto(sockfd,buff,strlen(buff)+1,0,(struct sockaddr *)&serv_storage,addr);
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continue;
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}
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char *token1,*token2;
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token1 = strtok(buffer," ");
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char req[10];
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strcpy(req,token1);
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token2 = strtok(NULL,"\n");
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strcpy(buffer,token2);
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char buffer_copy[BUFF_LEN];
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strcpy(buffer_copy,buffer);
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FILE *fp=fopen("cache.txt","r");
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char check[BUFF_LEN];
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strcpy(check,buffer);
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strcat(check,"-");
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strcat(check,req);
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printf("check : %s\n",check);
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bool flag = 0;
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char buff[BUFF_LEN], res[BUFF_LEN];
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bzero(res,BUFF_LEN);
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while(fp!=NULL && fgets(buff,BUFF_LEN,fp)){
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if(strncmp(buff,check,strlen(check))==0){
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while(1){
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bzero(buff,BUFF_LEN);
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fgets(buff,BUFF_LEN,fp);
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if(strncmp(buff,"---",3)==0) break;
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strcat(res,buff);
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}
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sendto(sockfd,res,strlen(res),0,(struct sockaddr *)&serv_storage,addr);
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printf("Response found in Cache\n");
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flag = 1;
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break;
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}
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}
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if(flag)
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continue;
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int count = 1;
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for(int i=0;i<strlen(buffer);i++)
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if(buffer[i] == '.')
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count++;
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printf("Total number of subdomains in the given domain name is %d\n",count);
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char a[count][SUB_DOMAIN_LEN];
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char *token;
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token = strtok(buffer_copy,".");
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for(int i=0;i<count;i++){
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strcpy(a[i],token);
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token = strtok(NULL,".");
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}
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char div_sub_domains[count][SUB_DOMAIN_LEN];
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strcpy(div_sub_domains[0],a[count-1]);
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for(int i=1;i<count;i++){
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strcpy(div_sub_domains[i],a[count-1-i]);
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strcat(div_sub_domains[i],".");
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strcat(div_sub_domains[i],div_sub_domains[i-1]);
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}
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for(int i=0;i<count;i++)
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printf("%s\n",div_sub_domains[i]);
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char nameservers[MAX_NAME_SERVERS][SUB_DOMAIN_LEN];
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int name_count = parse(".","",nameservers);
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for(int i=0;i<name_count;i++)
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printf("%s\n",nameservers[i]);
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for(int j=0;j<count-1;j++){
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char dup_nameservers[MAX_NAME_SERVERS][SUB_DOMAIN_LEN];
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for(int i=0;i<name_count;i++)
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strcpy(dup_nameservers[i],nameservers[i]);
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for(int i=0;i<name_count;i++)
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bzero(nameservers[i],SUB_DOMAIN_LEN);
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for(int i=0;i<name_count;i++){
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int temp = parse(div_sub_domains[j],dup_nameservers[i],nameservers);
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if(temp != 0){
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for(int i=0;i<temp;i++)
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printf("%s\n",nameservers[i]);
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name_count = temp;
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break;
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}
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}
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}
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char command[BUFF_LEN];
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for(int i=0;i<name_count;i++){
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strcpy(command,"nslookup -type=");
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strcat(command,req);
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strcat(command," ");
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strcat(command,buffer);
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strcat(command," ");
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strcat(command,nameservers[i]);
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printf("%s\n",command);
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const char * cmd = command;
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char result[BUFF_LEN] = "";
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FILE * out = popen(cmd, "r");
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char buff[BUFF_LEN];
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while (fgets (buff, 1000, out))
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strcat(result,buff);
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pclose(out);
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sendto(sockfd,result,strlen(result),0,(struct sockaddr *)&serv_storage,addr);
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FILE *fp=fopen("cache.txt","a");
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fprintf(fp,"%s-%s\n",buffer,req);
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fprintf(fp,"%s\n",result);
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fprintf(fp,"-------\n");
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fclose(fp);
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break;
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}
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}
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}
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close(sockfd);
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return 0;
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}

‎Sem-6/Networks Lab/Week-09/DNS-primer.pdf‎

67.2 KB
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‎Sem-6/Networks Lab/Week-09/Evaluation/Exp 9 Eval DNS_Modified.pdf‎

46 KB
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‎Sem-6/Networks Lab/Week-09/Evaluation/dns_client.c‎

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#include<stdio.h>
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#include<stdlib.h>
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#include<string.h>
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#include<netinet/in.h>
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#include<sys/socket.h>
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#include<sys/types.h>
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#include<netdb.h>
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#include<arpa/inet.h>
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#include<unistd.h>
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#define BUFF_LEN 4096
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#define MAX_SUB_buffer 20
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14+
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int main(){
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int sockfd = socket(PF_INET,SOCK_DGRAM,0);
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if(sockfd == -1){
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printf("Failed to create a socket\n");
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return 0;
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}
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else if(sockfd <= 0){
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printf("Invalid memory creation for socket. Try again\n");
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return 0;
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}
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struct sockaddr_in serv_addr;
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serv_addr.sin_family = AF_INET;
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serv_addr.sin_port = htons(1234);
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serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
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memset(serv_addr.sin_zero,0,sizeof(serv_addr.sin_zero));
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struct timeval read_timeout;
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read_timeout.tv_sec = 0;
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read_timeout.tv_usec = 100;
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int k = setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &read_timeout, sizeof(read_timeout));
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while(1){
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printf("Enter the command:");
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char buffer[BUFF_LEN];
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fgets(buffer,sizeof(buffer),stdin);
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int len = strlen(buffer);
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buffer[len-1] = '\0';
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int x = sendto(sockfd,buffer,strlen(buffer)+1,0,(struct sockaddr *)&serv_addr,sizeof(serv_addr));
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bzero(buffer,BUFF_LEN);
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while(1){
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if(recvfrom(sockfd,buffer,sizeof(buffer),0,NULL,NULL) > 0)
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break;
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//sleep(1);
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}
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printf("Message received from the server is : \n%s\n",buffer);
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if(!strcmp(buffer,"quit")){
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printf("Thank you for using the application\n");
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break;
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}
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bzero(buffer,BUFF_LEN);
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printf("Else Enter quit to close the communication\n");
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}
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close(sockfd);
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}

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