1. Internetworking: Concepts, Architecture, and Protocols
Chapter 20
Internetworking: Concepts, Architecture, and Protocols
© Bobby Hoggard, Department of Computer Science, East Carolina University
These slides may not be used or duplicated without permission

2. Extending a Network
A computer in a network can only communicate with other computers physically attached to the same network
Bridges (and other extension techniques) are used to connect networks of the same type; they cannot connect different types of networks
Ethernet
Ethernet
Token Ring

3. Extending a Network
Each network protocol has its own packet format and addressing scheme
To change from one to another, a translator is needed --- bridges do not do this
Ethernet
Wi-Fi
type
payload
src
addr
dest
ctrl
dur AP
addr
src
dest
seq
payload
14 bytes
bytes
24 bytes
bytes

4. Internetworking
Uses hardware and software to join together networks that are of different types
Additional hardware is used to interconnect the physical networks
Software on the attached computers provides universal service, and gives the illusion that the whole system is one large homogeneous network
Internetworks that are owned by private organizations and designed for use by only their employees is an intranet
The term Internet is used to refer to the global Internet

5. Routers
Routers connect networks that are of different types, so they operate as one large network
Hosts (devices connected to the routers) do not know whether they are connected to a single LAN segment or a large network connected by routers
A router can connect two LANs, two WANs, or a LAN and a WAN
Routers contain a processor, memory, and an I/O interface for each network to which it connects
Network 1
interface
processor
Network 2
interface
memory
unit
Network 3
interface

6. Routers Contain Protocol Software
Routers must rewrite a packet received from one network, into the format required by the destination network, and thus must understand the protocols from both networks
Ethernet
Wi-Fi A X
type
Hello
dest X
src A
type
Hello
src A
dest X
ctrl
dur AP 3
src A
dest X
seq
Hello
ctrl
dur AP 3
src A
dest X
seq
Hello

7. A Virtual Network
Routers create the illusion of a single, seemless communication system
Each computer is assigned an address, and any computer can send packets to any other
Internet protocol software hides the details of physical network connections, physical addresses and routing information

8. A Virtual Network
Routers create the illusion of a single, seemless communication system
Each computer is assigned an address, and any computer can send packets to any other
Internet protocol software hides the details of physical network connections, physical addresses and routing information
Net 2
Net 1
Net 4
Net 3
Net 5

9. Chapter 21 Internet Addressing
© Bobby Hoggard, Department of Computer Science, East Carolina University
These slides may not be used or duplicated without permission

10. Universal Addressing
To give the appearance of a universal network, all host computers must use a universal addressing scheme that's independent of the underlying hardware
MAC addresses cannot be used since the Internet consists of multiple network technologies, and each network technology can define its own MAC address
IPv4 uses 32-bit addresses and IPv6 uses 128-bit addresses
Transition to IPv6 is necessary because, although IPv4 allows for millions of networks, the Internet is growing exponentially and all IPv4 addresses are running out

11. IP Address Hierarchy IP addresses are split into two parts:
prefix or network address – identifies the physical network to which a host is attached (i.e. each network is assigned a unique number)
suffix or host address – identifies a specific computer on the network
network address
host address
Uniqueness is guaranteed because:
network addresses are coordinated globally to ensure that no two networks have the same number
host addresses are assigned by local network administrators, and they should ensure that no two computers in their network have the same suffix

12. IP Address Hierarchy
Example: Consider three networks, numbered 1, 2, and 3. Notice how local admins have assigned some of the same suffixes, yet the overall addresses remain unique
Network 2
Network 1 2 3 2 1
Network 3 1 5 2 2 1 1 1 3 3 5 3 2

13. Dotted Decimal Notation
Although IPv4 addresses are 32-bit binary numbers, software uses dotted decimal notation to make it easier to read and understand
Each byte of the 32-bit address is expressed as decimal value, and is separated by periods
byte 1
byte 2
byte 3
byte 4 5 8 2 1

14. Dotted Decimal Notation
The smallest value that can be expressed with one byte is = 0
The largest value that can be expressed with one byte is = 255
Thus, IP addresses range from to

15. How Many Bits?
How many bits are in the prefix (network), and how many are in the suffix (host)?
A large number of bits in the prefix allows:
A lot of networks
Few devices in each network
A large number of bits in the suffix allows:
A lot of devices in each network
Few networks
network address
host address
network addr
host address
millions of
values
few hundred
values
few hundred
values
millions of
values
One single choice isn't sufficient – the Internet consists of a few large networks and many small networks

16. Original Classes of IPv4 Addresses
Three classes were developed – which split the prefix/suffix after the 1st, 2nd, or 3rd byte
Class A - splits after first byte
Class B - splits after second byte
Class C - splits after third byte
Two more classes were developed for special purposes
Class D - multicast: used to deliver a packet to all computers in a predefined multicast group; restricted to individual sites
Class E - reserved for special purposes
You can determine which class the address belongs to by analyzing the first 4 bits

17. Original Classes of IPv4 Addresses
byte 2
Class A
network
host
byte 1
byte 3
byte 4
Class B 1
network
host
Class C 1
network
host
Class D 1
multicast
Class E 1
reserved (not assigned)