# Distance Vector Algorithm in C

## Distance Vector Routing Algorithm in C

In computer communication theory relating to packet-switched networks, a distance-vector routing protocol is one of the two major classes of routing protocols, the other major class being the link-state protocol. A distance-vector routing protocol uses the Bellman-Ford algorithm to calculate paths.

A distance-vector routing protocol requires that a router informs its neighbors of topology changes periodically and, in some cases, when a change is detected in the topology of a network. Compared to link-state protocols, which require a router to inform all the nodes in a network of topology changes, distance-vector routing protocols have less computational complexity and message overhead.

Distance Vector means that Routers are advertised as vector of distance and direction. 'Direction' is represented by next hop address and exit interface, whereas 'Distance' uses metrics such as hop count.

Routers using distance vector protocol do not have knowledge of the entire path to a destination. Instead DV uses two methods:

1. Direction in which or interface to which a packet should be forwarded.
2. Distance from its destination.

Examples of distance-vector routing protocols include Routing Information Protocol Version 1 & 2, RIPv1 and RIPv2 and IGRP. EGP and BGP are not pure distance-vector routing protocols because a distance-vector protocol calculates routes based only on link costs whereas in BGP, for example, the local route preference value takes priority over the link cost.

## Distance vector algorithm routing implementation in C

```#include<stdio.h>

struct node
{
unsigned dist[20];
unsigned from[20];
}rt[10];

int main()
{
int dmat[20][20];
int n,i,j,k,count=0;
printf("\nEnter the number of nodes : ");
scanf("%d",&n);
printf("\nEnter the cost matrix :\n");
for(i=0;i<n;i++)
for(j=0;j<n;j++)
{
scanf("%d",&dmat[i][j]);
dmat[i][i]=0;
rt[i].dist[j]=dmat[i][j];
rt[i].from[j]=j;
}
do
{
count=0;
for(i=0;i<n;i++)
for(j=0;j<n;j++)
for(k=0;k<n;k++)
if(rt[i].dist[j]>dmat[i][k]+rt[k].dist[j])
{
rt[i].dist[j]=rt[i].dist[k]+rt[k].dist[j];
rt[i].from[j]=k;
count++;
}
}while(count!=0);
for(i=0;i<n;i++)
{
printf("\n\nState value for router %d is \n",i+1);
for(j=0;j<n;j++)
{
printf("\t\nnode %d via %d Distance%d",j+1,rt[i].from[j]+1,rt[i].dist[j]);
}
}
printf("\n\n");
}
```

## Makefile

```a.out:distanceVector.c
gcc -ggdb distanceVector.c
PHONY:clean
clean:
rm a.out *~```

## Example output

Enter the number of nodes : 4

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

State value for router 1 is

node 1 via 1 Distance0
node 2 via 2 Distance3
node 3 via 3 Distance5
node 4 via 2 Distance4

State value for router 2 is

node 1 via 1 Distance3
node 2 via 2 Distance0
node 3 via 4 Distance3
node 4 via 4 Distance1

State value for router 3 is

node 1 via 1 Distance5
node 2 via 4 Distance3
node 3 via 3 Distance0
node 4 via 4 Distance2

State value for router 4 is

node 1 via 2 Distance4
node 2 via 2 Distance1
node 3 via 3 Distance2
node 4 via 4 Distance0

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haribabu 5 years ago

mastu undi ra bai program.........

vygi 5 years ago

i want in java

prabhakar gouda 5 years ago from Bangalore Author

@haribabu thanks ra

prabhakar gouda 5 years ago from Bangalore Author

hey vygi if you know java then you can convert it into java right .... it is not a big deal to convert to c to java

Dan P 5 years ago

are the [20]'s assuming that there won't be more than 20 routers? How would you do that dynamically if you can't guarantee that?

4 years ago

Shouldn't the example cost matrix be symmetric? Cost[2][3] is 99 (99 means "infinity" here, I guess) but Cost[3][2] is 4...

Last post agreed Cost[2][3]is ? then how come the value ofCost[3][2] is 4?????????????

DjRocky 4 years ago

Wow ............. Idiot's !

Sid Vj 4 years ago

I deserve to be winner of big boss. But don't know why Jui is winner. Anyways love you Sunny.

raj 4 years ago

implementation is nice bt starting one is bad

raj 4 years ago

i understood jst nw

kishore 4 years ago

I get an infinite loop on cost matrix

0 6 2 7

4 0 4 -1

8 5 0 2

7 -1 7 0

???

Help!

kishore 4 years ago

could you brief how this works

thanks!

yo baby 4 years ago

thanx

Quit 4 years ago

@Kishore

its not for negative costs !

its only for positive values.

if you want it for negative costs, then implement it through dijkstra algorithm.

thanks. :)

Tarun Kumar 4 years ago

hey guys can you give me a matrix or scenario where distance vector does not work, i am doing project on DV algo and i need to prove that in these kind of cases DV fails to work.

prabhakar gouda 4 years ago from Bangalore Author

Hey guy please take tarun help for more efficient code .... Thanks Tarun

Tarun Kumar 4 years ago

I would definitely love to help but first give me a matrix where DV fails to work,

i want this to push my code to a limit and want to check how efficient it is .

prabhakar gouda 4 years ago from Bangalore Author

@tarun can you please try for the matrix which kishore has mentioned

santhosh.m 4 years ago

unknown 4 years ago

I need in java can u try it...