Advanced Computer Networks: Lecture 20 - Dr. Amir Qayyum

Advanced Computer Networks: Lecture 20. This lecture will cover the following: Virtual Private Networks - VPN; IP tunneling and IP tunnel in VPNs; Bellman-Ford algorithm; Dijkstra’s algorithm;...

CS716 Advanced Computer Networks By Dr. Amir Qayyum Lecture No. 20 Virtual Private Networks ­ VPN C Physical links A B Corporation X private network K L M Corporation Y private network (a) K C L Physical links A M B Virtual circuits (b) IP Tunneling Data IP Data IP  IP  Multicast Multicast VU IP IP IP  IP  Multicast Multicast IPv4 Da ta IP UET IP IP  IP  Multicast Multicast MAJU IP Tunnel in VPNs • Virtual point­to­point link between a pair of nodes  separated by many networks Network R1 Internetwork R2 Network 10.0.0.1 IP header, Destination = 2.x IP header, Destination = 10.0.0.1 IP header, Destination = 2.x IP payload IP header, Destination = 2.x IP payload IP payload Routing Pir Wadhai Islamabad Rawal  Dam Rawalpindi Faizabad Airport • A stranger appears and asks “Airport ?” • Which way do you point ? Routing Overview A C B E F D Bellman­Ford 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 Bellman­Ford Algorithm A Source Infinity Infinity Infinity 8 C C Infinity Infinity 3 B B B C Infinity Infinity 7 2 E E E Infinity 5 4 Infinity 1 1 B Dest Dest Dest Dest Destination E Dest Dest A A • 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 one­hop paths from N – Loop n­1 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 ? 10 Dijkstra’s Algorithm 3 7 2 6 10 8 10 11 12 13 14 15 11 .. .Lecture? ?No.? ?20 Virtual Private Networks ­ VPN C Physical links A B Corporation X private network K L M