2. Program for character stuffing​ 3- Connect the computers in Local 4.

n Local 4.To configure DHCP and DNS server for a given network in packet tracer simulator tool.
#include<stdio.h> Area Network. DHCP (Dynamic Host Configuration Protocol) is a protocol that lets network administrators manage centrally and automate
#include<conio.h> On the Host Computer (Sharing the assignment of Internet Protocol (IP) addresses in an organization's network. If a machine uses Internet's set of protocol
Internet): (TCP/IP), each machine that can connect to the Internet needs a unique IP address. When an organization sets up its
#include<string.h>
Log in as Administrator or Owner. computer users with a connection to the Internet, an IP address must be assigned to each machine. Without DHCP, the IP
#include<process.h> address must be entered manually at each computer and, if computers move to another location in another part of the
void main() Go to: Start > Control Panel > Network
and Internet Connections > Network network, a new IP address must be entered. DHCP lets a network administrator supervise and distribute IP addresses from
{ Connections. a central point and automatically sends a new IP address when a computer is plugged into a different place in the network.
int i=0,j=0,n,pos; Right-click the Internet connection IP Address Allocation Mechanism DHCP supports three mechanisms for IP address allocation. •
char a[20],b[50],ch; (e.g., dial-up, Ethernet). Automatic allocation: DHCP assigns a permanent IP address to a host. •
clrscr(); Click Properties. Dynamic allocation: DHCP assigns an IP address to a host for a limited period of time (or until the host explicitly
Go to the Advanced tab. relinquishes the address). •
printf("enter string\n");
Check: "Allow other network users to Manual allocation: Host's IP address is assigned by the network administrator, and DHCP is used simply to convey the
scanf("%s",&a); assigned address to the host. A particular network will use one or more of these mechanisms, depending on the policies of
connect through this computer's
n=strlen(a); the network administrator.
Internet connection".
printf("enter position\n"); (If using dial-up) Check:​ Messages Used by DHCP:
scanf("%d",&pos); "Establish a dial-up connection • DHCP Discover - Client broadcast to locate available servers. It is assumed atleast one of the servers will have
if(pos>n) whenever a computer on my network resources to fulfill the request.( may include additional pointers to specific services required eg. particular subnet, minimum
{ attempts to access the Internet" time limit etc ).
(optional). • DHCP Offer - Server to client in response to DHCP Discover with offer of configration parameters.
printf("invalid position, Enter again :");
Click OK. • DHCP Request - Client broadcast to servers requesting offered parameters from one server and implicitly declining offers
scanf("%d",&pos); from all others.( also important in case of lease renewal if the alloted time is about to expire ).
When prompted:​
} • DHCP Decline - Client to server indicating configration parameters invalid.
"Your LAN adapter will be set to IP
printf("enter the character\n"); 192.168.0.1. Other PCs may lose • DHCP Release - Client to server relinquishing network address and cancelling current lease.( in case of a graceful shut
ch=getche(); connectivity. Continue?"​ down DHCP server is sent a DHCP Release by the host machine).
b[0]='d'; Click Yes. • DHCP Ack - Server to client with configration parameters, including committed Network address.
Now, Internet is shared. The host LAN • DHCP Nack - Server to client refusing request for configuration parameters (eg. requested network address already
b[1]='l';
adapter is set to: allocated).
b[2]='e'; Timers Used Note:
b[3]='s'; IP Address: 192.168.0.1​
that lease time is the time specified by the server for which the services have been provided to the client.
b[4]='t'; Subnet Mask: 255.255.255.0 • Lease Renewal Timer - When this timer expires machine will ask the server for more time sending a DHCP Request.
b[5]='x'; • Lease Rebinding Timer - Whenever this timer expires, we have not been receiving any response from the server and so
j=6;
On the Client Computer we can assume the server is down. Thus send a DHCP Request to all the servers using IP Broadcast facility. This is only
while(i<n) (Receiving Internet): point of difference between Lease renewal and rebinding.
Log in as Administrator or Owner. • Lease Expiry Timer - Whenever this timer expires, the system will have to start crashing as the host does not have a
{
Go to: Start > Control Panel > Network valid IP address in the network.
if(i==pos-1) and Internet Connections > Network Timer Configuration Policy
{ Connections. The timers have this usual setting which can be configured depending upon the usage pattern of the network.
b[j]='d'; Right-click Local Area Connection → An example setting has been discussed below.
b[j+1]='l'; Properties. Lease Renewal = 50 % Lease time
b[j+2]='e'; On General tab, select Internet Lease Rebinding = 87.5 % Lease time
Protocol (TCP/IP) → Click Properties. Lease Expiry = 100 % Lease time Practical:
b[j+3]=ch;
Select:
b[j+4]='d'; Obtain an IP address automatically DHCP ON PACKET TRACER STEPS ARE AS FOLLOWS:
b[j+5]='l'; Assign manually: 1. Let us make a topology with one router on which we will apply DHCP and several client PCs. More like this one,
b[j+6]='e'; IP Address: 192.168.0.x (e.g., 2. Now, we will apply DHCP on the router.The commands in sequence are as follows.
j=j+7; 192.168.0.2) Router>en
} Subnet Mask: 255.255.255.0 Router#conf t
if(a[i]=='d' && a[i+1]=='l' && Default Gateway: 192.168.0.1 Router(config)# int fa 0/0
Click OK to close all dialogs. Router(config-if)# ip address 192.168.11 255.255.255.0
a[i+2]=='e')
Exit Control Panel. Router(config-if)# no shut % LINK-5-CHANGED:
{ % LINK-5-CHANGED:Interface FastEthernet 0/0, change state to up %LINEPROTO-5-UPDOWN:
b[j]='d'; _____________________________
Line protocol on Interface FastEthernet 0/0, change state to up
b[j+1]='l'; router (config-if)# ip dhcp pool cisco
10. To configure dynamic routing
b[j+2]='e'; router (dhp-config)# network 192.168.1.0 255.255.255.0
j=j+3;
}
🔧
protocols in packet race tool.
Steps:
Step 1: Set up the Network Topology:
router(dhcp-config)#default-router 192.168.1.1
router(dhcp-config)# exit
router(config)# ip dhcp excluded-address 192.168.1.4 192.168.1.7
b[j]=a[i];
router(config)#exit
i++; Create a simple topology by adding (i)command “ip dhcp pool cisco”, we are creating a pool for DHCP called cisco.
j++; devices like routers, switches, and (ii)command “default-router “ we are telling the DHCP about the default route to follow.
} PCs. (iii)“ip dhcp excluded-addresses x-x”, where x is the starting and ending IP address respectively.
b[j]='d'; Connect them using appropriate We are basically reserving some IPs for our use. It can be used to attach printers, or assign it to some specific users for
cables (copper straight-through or security purposes.
b[j+1]='l'; crossover, depending on device
b[j+2]='e'; 3.Now, open the PC. Click on IP Configuration. Select from Static to DHCP
types). 4. And after the DHCP request is completed you will see the following screen.
b[j+3]='e';
b[j+4]='t'; Step 2: Assign IP Addresses:
b[j+5]='x'; Assign IP addresses to all the 7. To configure NAT (Network Address Translation) for a given Ro(config-if)# no shutdown
b[j+6]='\0'; interfaces of routers and PCs. network in the Packet Tracer simulator tool.
Ensure each device has a unique IP Ro(config-if)# exit
printf("\nframe after stuffing:\n"); Code / Steps:
address within the correct subnet.​ Ro(config)# ip route 50.0.0.0
Computer Networks Lab LAB Configuration on Router R1:
MANUAL 255.0.0.0 20.0.0.2
Example: Router> enable
17 Router1 Fa0/0: 192.168.1.1/24 Explanation:
printf("%s",b); Router# configure terminal Since there is no direct route for 10.0.0.2,
Router2 Fa0/0: 192.168.2.1/24
getch(); Step 3: Enable Routing on Routers Router(config)# hostname R1 external networks like 30.0.0.0 will only
Program for bitstuffing Click on the router.​ R1(config)# interface FastEthernet 0/0 recognize it as the web server IP 50.0.0.1
#include <stdio.h> R1(config-if)# ip address 10.0.0.1 255.0.0.0
Go to the CLI tab at the bottom of the (which is translated using NAT).
#include <string.h>
void bitStuffing(int N, int arr[]) { Packet Tracer window.​ R1(config-if)# no shutdown To test the setup:
int brr[30]; R1(config-if)# exit Open any computer from the external
int i = 0, j = 0, k; Step 4: Enter Privileged EXEC Mode network (connected to 30.0.0.0)
R1(config)# interface Serial 0/0/0
while (i < N) {
Step 5: Configure OSPF Routing R1(config-if)# ip address 20.0.0.2 255.0.0.0 Go to Command Prompt
if (arr[i] == 1) {
int count = 1; Protocol Type:
R1(config-if)# no shutdown
brr[j] = arr[i]; bash ping 50.0.0.1
for (k = i + 1; arr[k] == 1 && CopyEdit R1(config-if)# exit
Expected Output:
k < N && count < 5; k++) { configure terminal R1(config)# ip route 30.0.0.0 255.0.0.0 20.0.0.1
Pinging 50.0.0.1 with 32 bytes of
j++; router ospf <process-id> R1(config)# ip nat inside source static 10.0.0.2
brr[j] = arr[k]; network <network-address> data:
count++; 50.0.0.1
<wildcard-mask> area <area-id> Reply from 50.0.0.1: bytes=32
if (count == 5) { R1(config)# interface FastEthernet 0/0
j++; time<1ms TTL=64
Replace: R1(config-if)# ip nat inside
brr[j] = 0; Ping statistics for 50.0.0.1:
} <process-id> with any unique R1(config-if)# exit
number (e.g., 1) Packets: Sent = 4, Received =
i = k; R1(config)# interface Serial 0/0/0
} <network-address> and 4, Lost = 0 (0% loss)
} else { <wildcard-mask> with your actual R1(config-if)# ip nat outside
Now ping from inside network:
brr[j] = arr[i]; network info​ R1(config-if)# exit ping 10.0.0.2
} <area-id> with the OSPF area Configuration on Router Ro:
i++; Expected Output:

}
j++; ✅
(usually 0 for backbone area)​
Example:
Router> enable
Router# configure terminal
Ping statistics for 10.0.0.2:
Packets: Sent = 4, Received =
router ospf 1
network 192.168.1.0 0.0.0.255 Router(config)# hostname Ro 4, Lost = 0 (0% loss)
for (i = 0; i < j; i++)
printf("%d", brr[i]); area 0 Ro(config)# interface FastEthernet 0/0 Conclusion:
} network 192.168.2.0 0.0.0.255 Ro(config-if)# ip address 30.0.0.1 255.0.0.0 This demonstration shows how companies use
int main() { area 0 Ro(config-if)# no shutdown NAT (Network Address Translation) to hide
int N = 6; Final Step:
int arr[] = {1, 1, 1, 1, 1, 1}; Ro(config-if)# exit internal IP addresses from the outside world,
Save the configuration:​
bitStuffing(N, arr); write memory Ro(config)# interface Serial 0/0/0 while still allowing external access to services
return 0; copy running-config through a public IP address.
} Ro(config-if)# ip address 20.0.0.1 255.0.0.0
startup-config
8- Write a program to implement TCP & UDP Sockets. 9. C Program to Transmit a Character, String, and File
Data using Static Array (Simulated in Packet Tracer
Theory/concept:- 6: Write a CAD code to get the MAC (physical) address of the Style)
system using ARP and to simulate it in a given network
Below find an example of a very simple client-server program in C. Basically according to requirements in the Packet Tracer simulator. #include <stdio.h>
the client connects to the server, the #include <fcntl.h>
server sends the message “Hello World”, and the client prints the received : #include <unistd.h>
ARP:​
#include <string.h>
The Address Resolution Protocol (ARP) is a network protocol
Server Code
used to map IP addresses (logical addresses) to MAC
int main() {
addresses (physical addresses) in a Local Area Network (LAN).
#include <stdio.h> int fd = open("/dev/ttyS0", O_WRONLY);
#include <sys/socket.h> if (fd == -1) {
#include <netinet/in.h> Working: perror("Error Opening Port");
#include <string.h> return 1;
}
int main(){ When a device (Host A) wants to communicate with another
int welcomeSocket, newSocket; device (Host B) in the same network, it needs to know the MAC char ch = 'A';
char buffer[1024]; address of Host B. char str[] = "Hello RS-232";
struct sockaddr_in serverAddr; char filedata[1024] = "Sample file content\n";
struct sockaddr_storage serverStorage;
socklen_t addr_size; Host A checks its ARP cache. write(fd, &ch, 1);
write(fd, str, strlen(str));
welcomeSocket = socket(PF_INET, SOCK_STREAM, 0); write(fd, filedata, strlen(filedata));
If the MAC address is not found, Host A sends a broadcast ARP
request to all devices on the network.
serverAddr.sin_family = AF_INET; close(fd);
serverAddr.sin_port = htons(7891); return 0;
serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1"); The device with the matching IP address (Host B) replies with an }
memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero); ARP reply containing its MAC address.​
Receiver Code
bind(welcomeSocket, (struct sockaddr *) &serverAddr, Host A stores this address in its ARP cache for future use.​
sizeof(serverAddr)); How to See ARP Table:​ #include <stdio.h>
Type arp -a in the command prompt and press Enter. The #include <fcntl.h>
if(listen(welcomeSocket,5)==0) resulting ARP table will be displayed containing the MAC #include <unistd.h>
printf("Listening\n"); addresses. #include <string.h>
else
printf("Error\n"); int main() {
___________________________________-_______ int fd = open("/dev/ttyS0", O_RDONLY);
addr_size = sizeof serverStorage; char ch;
newSocket = accept(welcomeSocket, (struct sockaddr *) &serverStorage, char str[50], filedata[1024];
&addr_size); 7. To configure a router using the command line interface
(CLI) and also observe the data gram formats in the Packet read(fd, &ch, 1);
strcpy(buffer,"Hello World\n"); Tracer simulator tool. read(fd, str, sizeof(str));
send(newSocket,buffer,13,0); read(fd, filedata, sizeof(filedata));

return 0; Theory: printf("Received Character: %c\n", ch);

} printf("Received String: %s\n", str);
printf("Received File Data: %s\n", filedata);
A router is a device that transfers data packets between two
/****************** CLIENT CODE ****************/ different networks. A router joins two or more distinct networks close(fd);
by acting as a mediator device. Its function is called routing. return 0;
#include <stdio.h> }
#include <sys/socket.h>
#include <netinet/in.h> Basic Router Configuration with Commands: Router R1 Configuration
#include <string.h>
enable​ enable
int main(){ (Entering privileged EXEC mode)​ configure terminal
int clientSocket; hostname R1
char buffer[1024]; configure terminal​ interface fastEthernet 0/0
struct sockaddr_in serverAddr; (Entering global configuration mode)​ ip address 192.168.1.1 255.255.255.0
socklen_t addr_size; no shutdown
hostname RouterA​ interface serial 0/0/0
clientSocket = socket(PF_INET, SOCK_STREAM, 0); (Setting the hostname)​ ip address 10.0.0.1 255.255.255.0
no shutdown
serverAddr.sin_family = AF_INET; interface FastEthernet 0/0​ ip route 192.168.2.0 255.255.255.0 10.0.0.2
serverAddr.sin_port = htons(7891); (Entering interface configuration mode)​
serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1"); Router R2 Configuration
memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero); ip address 192.168.1.1 255.255.255.0​
(Assigning IP address to the interface)​ enable
addr_size = sizeof serverAddr; configure terminal
connect(clientSocket, (struct sockaddr *) &serverAddr, addr_size); no shutdown​ hostname R2
(Activating the interface)​ interface fastEthernet 0/0
recv(clientSocket, buffer, 1024, 0); ip address 192.168.2.1 255.255.255.0
printf("Data received: %s", buffer); no shutdown
exit​
interface serial 0/0/0
(Exiting interface configuration mode)​
return 0; ip address 10.0.0.2 255.255.255.0
} no shutdown
ip route 0.0.0.0 0.0.0.0 192.168.1.254​ ip route 192.168.1.0 255.255.255.0 10.0.0.1
(Setting the default gateway route)​

write memory​
(Saving the configuration)

PC Configuration:
PC1 IP: 192.168.1.2/24​
Gateway: 192.168.1.1​

PC2 IP: 192.168.1.3/24​

Gateway: 192.168.1.1​