04/11/23 1

Tunneling

When source & destination are on the same type of network but there is a different network in-between, tunneling is used.

04/11/23 2

04/11/23 3

Internetwork Routing

A

B

E

F

DC

An Internetwork

1

23

54

Gateway

Network

A B

E F

DC

A Graph of the Internetwork

04/11/23 4

Difference between internetworking & intranetworking Crossing international boundaries

Cost QOS Time

04/11/23 5

Fragmentation

Various causes for each network to imposes MAXSIZE on its packets

1. Hardware

2. Operating system

3. Protocols

4. Compliance with some (inter)national Standard

5. Desire to reduce error induced retransmissions to some level.

6. Desire to prevent one packet from occupying the channel too long.

04/11/23 6

Need of Fragmentation?

When a large packet wants to travel through a network whose MAXSIZE is too small. Avoid sending packets to those networks.

Destination network itself cant handle large packets. Fragmentation.

The Gateways are allowed to break-up the packets into fragments, sending each packet as a separate internet packet.

04/11/23 7

Recombining the Fragments

Transparent Fragmentation

Non- Transparent Fragmentation

04/11/23 8

Transparent Fragmentation

G1 G2

Packet

Network 1

G1 fragments a

large packet

G2 reassembles the packets

G3 G4

Network 2

G3 fragments again

G4 reassembles again

04/11/23 9

Drawbacks of Transparent Fragmentation

1. Exit gateway must know when it has received all the fragmented packets.

2. Performance loss, because all packets must exit via the same gateway.

3. Overhead required to repeatedly reassemble & refragment large packet.

04/11/23 10

Non Transparent Fragmentation

Stops recombining fragments at any intermediate gateways

G1 G2 G3 G4

Packet

G1 fragments a large packet The fragments are not reassembled until

the final destination is reached.

04/11/23 11

Disadvantage of Non-transparent fragmentation

Increases overhead.

04/11/23 12

Numbering Fragments

Tree Elementary Packet Size

04/11/23 13

Numbering fragments using TREES

0

0.0 0.1 0.2 0.3

0.0.0 0.0.1 0.1.0 0.1.1 0.2.0 0.3.00.2.1 0.3.1

04/11/23 14

Elementary Fragment Size

Packet number

EDCBA0027 HGF0527

HGFEDCBA0027

JIHGFEDCBA1027

End of packet bit

Number of the first elementary fragment in this packet

JI1827

JI1827

Header

1 byte

Header

Header

Header Header

Header

a) Fragmentation when elementary data size is 1 byte, b) Max packet size is 8 bytes

c) Packet size is 5 bytes.

a)

b)

c)

04/11/23 15

Firewalls

                                               

                                                                           

04/11/23 16

Inside LAN Outside LAN

Packet Filtering Router

Application Gateway

Packet Filtering Router

Connections to Outside World

A Firewall Consisting of two Packet filtering routers & an Application Gateway