1. Advanced Computer Networks
CS716
Advanced Computer Networks
By Dr. Amir Qayyum 1

2. Lecture No. 20

3. Virtual Private Networks - VPN

4. IP Tunneling IP Multicast IP Multicast IPv4 VU UET IP Multicast MAJU
Data IP
IP Multicast
IP Multicast
Data IP IP
IPv4
Data IP VU
UET
IP Multicast
MAJU

5. IP Tunnel in VPNs
Virtual point-to-point link between a pair of nodes separated by many networks
Network 1 R1
Internetwork R2
Network 2
IP header ,
IP header ,
IP header ,
Destination = 2.x
Destination =
Destination = 2.x
IP header ,
IP payload
IP payload
Destination = 2.x
IP payload

6. Routing A stranger appears and asks “Airport ?”
Islamabad
Pir Wadhai
Rawal Dam
Rawalpindi
Faizabad
Airport
A stranger appears and asks “Airport ?”
Which way do you point ?

7. Routing Overview

8. Bellman-Ford Algorithm
For every node N
For each directed pair (B,C)
Is the path B  N  …C better than B .C ?
Is cost BNdest smaller than previously known?
For N nodes
Uses an NxN matrix of (distance, successor) values

9. Bellman-Ford Algorithm
Source A B
Infinity
Infinity
Infinity 6 2
Infinity
1 Dest
5 Dest
1 Dest
3 B
Infinity
5 Dest
7 E
1 Dest
3 B
8 C
4 A
7 E
8 C
3 B
1 Dest
4 A
6 E 1 1 1 C E
Destination
Infinity
Infinity 2 5
After n iterations, nodes at distance n hops along the shortest path have correct information

10. Dijkstra’s Algorithm From node N
Start with S = {N} and one-hop paths from N
Loop n-1 times
Add closest outside node M to S
For each node P not in S
Is the path N M P better than N P ?

11. Dijkstra’s Algorithm 3 1 3 4 7 1 6 2 4 2 11 9 2 2 7 7 3 1 2 2 6 9 4 12 13 6 1 10 15 3 8 3 5 8 10 14