CS716
Advanced Computer Networks
By Dr. Amir Qayyum
1
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)
3
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
4
IP Tunnel in VPNs
• Virtual pointtopoint link between a pair of nodes
separated by many networks
Network 1
R1
Internetwork
R2
Network 2
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
5
Routing
Pir Wadhai
Islamabad
Rawal
Dam
Rawalpindi
Faizabad
Airport
• A stranger appears and asks “Airport ?”
• Which way do you point ?
6
Routing Overview
A
1
3
4
C
6
1
B
9
E
2
F
1
D
7
BellmanFord Algorithm
• For every node N
– For each directed pair (B,C)
• Is the path B N …C better than B .C ?
• Is cost BNdest smaller than previously known?
• For N nodes
– Uses an NxN matrix of (distance, successor) values
8
BellmanFord Algorithm
A
Source
Infinity
Infinity
Infinity
8
8
6
C
C
Infinity
Infinity
3
3
3
1
B
B
B
1
C
Infinity
Infinity
7
7
6
2
2
E
E
E
Infinity
5
5
4
4
Infinity
1
1
1
1
B
Dest
Dest
Dest
Dest
1
Destination
E
Dest
Dest
A
A
5
• After n iterations, nodes at distance n hops along the shortest
path have correct information
9
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
1
2
3
2
4
2
9
7
7
1
3
2
2
6
4
1
6
10
8
1
2
3
4
5
6
7
8
9
3
10 11 12 13 14 15
11