Computer Networks - (LAB PROGRAMS)

Aim:

☛ Implement distance vector routing algorithm for obtaining routing tables at each node.

Solution :

Week 6

Implement Distance vector routing algorithm

Input Graph:

Source Code:

File Name: distance_vector_routing.c

#include<stdio.h>

// Structure to represent the routing table of each router
struct RoutingTable {
    unsigned distance[20];  // Distance to each destination node
    unsigned nextHop[20];   // Next hop to reach each destination node
} rt[10];

int main() {
    int costMatrix[20][20];  // Cost matrix input by user
    int numNodes;            // Number of routers/nodes in the network
    int i, j, k;             // Loop counters
    int updated;             // Flag to check if any update is made in the routing table

    // Read the number of routers
    printf("\nEnter the number of nodes (routers): ");
    scanf("%d", &numNodes);

    // Read the cost matrix
    printf("\nEnter the cost matrix:\n");
    for (i = 0; i < numNodes; i++) {
        for (j = 0; j < numNodes; j++) {
            scanf("%d", &costMatrix[i][j]);

            // Distance from a node to itself is 0
            if (i == j) {
                costMatrix[i][j] = 0;
            }

            // Initialize routing table
            rt[i].distance[j] = costMatrix[i][j]; // Initial distance
            rt[i].nextHop[j] = j;                // Initial next hop (direct connection)
        }
    }

    // Apply Distance Vector Routing algorithm (Bellman-Ford logic)
    do {
        updated = 0;  // Assume no updates

        for (i = 0; i < numNodes; i++) {
            for (j = 0; j < numNodes; j++) {
                for (k = 0; k < numNodes; k++) {
                    // Check if the path from i to j via k is shorter
                    if (rt[i].distance[j] > costMatrix[i][k] + rt[k].distance[j]) {
                        rt[i].distance[j] = costMatrix[i][k] + rt[k].distance[j];
                        rt[i].nextHop[j] = k; // Update next hop
                        updated = 1;          // Mark that an update occurred
                    }
                }
            }
        }
    } while (updated);  // Repeat until no updates

    // Print final routing tables
    for (i = 0; i < numNodes; i++) {
        printf("\nRouting Table for Router %d:\n", i + 1);
        printf("Destination\tNext Hop\tDistance\n");
        for (j = 0; j < numNodes; j++) {
            printf("     %d\t\t   %d\t\t   %d\n", j + 1, rt[i].nextHop[j] + 1, rt[i].distance[j]);
        }
    }

    printf("\n");
    return 0;
}

Output:


$ gcc distance_vector_routing.c
$ ./a.out

Enter the number of nodes (routers): 4

Enter the cost matrix:
0 3 5 99
3 0 99 1
5 4 0 2
99 1 2 0

Routing Table for Router 1:
Destination     Next Hop        Distance
     1             1               0
     2             2               3
     3             3               5
     4             2               4

Routing Table for Router 2:
Destination     Next Hop        Distance
     1             1               3
     2             2               0
     3             4               3
     4             4               1

Routing Table for Router 3:
Destination     Next Hop        Distance
     1             1               5
     2             4               3
     3             3               0
     4             4               2

Routing Table for Router 4:
Destination     Next Hop        Distance
     1             2               4
     2             2               1
     3             3               2
     4             4               0

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