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

Lecture No. 20

Virtual Private Networks - VPN

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

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 10.0.0.1 IP header , IP header , IP header , Destination = 2.x Destination = 10.0.0.1 Destination = 2.x IP header , IP payload IP payload Destination = 2.x IP payload

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 ?

Routing Overview

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

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

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 ?

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