1. Addressing
The ‘What’ and ‘Where’ of
Communication

2. Addressing
 Addressing is necessary for any
communication
– To talk: Appearance, name, …
– To call: Telephone numbers
– To mail: Postal address
– To visit: Postal address + directions
– To E-Mail: E-Mail addresses
– To instant message: ICQ#, AIM ID, etc.
 These ‘addresses’ allow us to uniquely
identify the entity with which we wish to
communicate

3. Addressing a la Shoch
 Name/Identifier: What
– Names normally identify the entity
– If an entity moves, the name/identity will remain
the same
 Address: Where
– Addresses identify the location of the entity
– If an entity moves, the address will change
 Route: How to get there
– Routes identify the path to get to an entity
– If an entity moves, the route will change

4. Addressing
 Addressing deals with how to define an
entity’s location (uniquely)
 Addressing is necessary for message
delivery
– An address is the start and end point for
the route
• However, routing is another subject
– Where do we want the message to go?

5. Addresses
 We have already seen MAC addresses (for
Ethernet and some other LANs):
– e.g. 02-60-8C-08-E1-0C
– 6 octet address
– Globally unique
– Defined statically by the hardware manufacturer
 Most people are familiar with the IP
addresses used by TCP/IP networks:
– e.g. 137.207.32.2
– 4 octet address
– Not necessarily globally unique
– Defined dynamically by DHCP servers or
negotiated by the operating system

6. IP Addressing
A Closer Look

7. IP Addresses
 TCP/IP networks use IP for the network layer
protocol
 IP defines 4 octet addresses
– 4 billion possible addresses
 Usually written in the form A.B.C.D
– A, B, C, and D are each 1 octet (0-255), normally
written in decimal notation
– Thus, IP addresses fall in the range:
0.0.0.0 – 255.255.255.255

8. IP Addresses
 Originally intended for separate
internets (interconnected LANs)
– Thus, the 32 bit size was not a concern
– 48 bits is generally considered a fairly safe
size for globally unique addressing
– Computers connected to ARPANET (and
later incarnations) were just given
consecutive addresses
1.0.0.0, 1.0.0.1, 1.0.0.2, …

9. IP Addresses
 Any computer connected to a TCP/IP
network (e.g. the Internet) must have an
IP address
 Further, any network interface card
(NIC) using TCP/IP to access an
network (e.g. the Internet) must have a
different IP address

10. IP Addresses
 Even though there are 4 billion possible
IP addresses, they are running out
 Here’s why:
– Some of the bits are dedicated to header
information (discussed later)
• ½ the addresses for each lost bit
– Addresses are categorized, and some of
the categories are running out of
addresses (while others are not)

11. Non-Classed Addresses
 Part of the address represented the network
the computer resided on, and part
represented the computer itself
– Network: 7 bits (up to 128 networks)
– Computer: 24 bits (up to 1.6 million computers on
each network)
 Since there were very few networks on
ARPANET originally, this wasn’t a problem

12. Address Classes
 When private organizations started
joining the Internet, the needs became
obvious
– Some (fewer) networks have multitudes of
computers (thousands)
• e.g. The @Home network
– Some (many) networks have very few
computers (a few hundred or less)
• e.g. The Windsor Police Department

13. Address Classes
 Quickly, the addresses were separated
into 3 classes (plus room for more
classes if needed):
– Class A: Fewer networks, many nodes
– Class B: Medium networks, medium nodes
– Class C: Many networks, fewer nodes

14. IP Address Classes
Class A:
bit index: 0 1-7 8-31
0 network host (machine)
Class B:
bit index: 0 1 2-15 16-31
1 0 network host
Class C:
bit index: 0 1 2 3-23 24-31
1 1 0 network host

15. IP Address Classes
 Class A:
– Range: 1.0.0.0 – 126.0.0.0
– Networks: 128 max, Machines: 65537-1.6 million
– e.g. huge networks, such as large
military/government organizations (e.g. FBI), the
@Home network, etc…
 Class B:
– Range: 128.1.0.0 – 191.255.0.0
– Networks: 16384 max, Machines: 257-65536
– e.g. Internet service providers (ISPs) (dial-up)
 Class C:
– Range: 192.1.0.0 – 223.255.255.0
– Networks: 2 million max, Machines: 1-256
– e.g. Small businesses

16. IP Address Classes
 The IP address classes are self-identifying
– Which means that given the address, you can
determine what class an address is
• Actually, using only the first number
– Examples:
• 137.207.32.2 (server.uwindsor.ca)
– 137 -> Class B
• 24.0.0.1 (@Home DHCP server)
– 24 -> Class A

17. Other IP Address Classes
Class D:
bit index: 0 1 2 3 4-31
1 1 1 0 Multicast group address
•These addresses are used to represent multicast groups
•Discussed later
Class E:
bit index: 0 1 2 3 4 5-31
1 1 1 1 0 Reserved for future use
•These addresses were left open to be used and divided
into classes as needed

18. Special IP Addresses
 0.0.0.0: Used to indicate that this machine is
without an assigned IP
– Used during bootstrapping (e.g. requesting an IP
from a DHCP server)
 <all 0s (binary)><hostID>: Used to send
messages to some machine on this network
 255.255.255.255: Used to send broadcast
messages across this machine’s network
 <netID><all 1s (binary)>: Used to send
broadcast messages to the specified network
 127.0.0.1: Used to send messages back to
this machine (called loopback or localhost)

19. IP Addressing Comments
 In IP addressing:
– 0’s usually represent ‘this’
– 1’s usually represent ‘all’
 Broadcasting, although discussed here
in terms of addressing, will be
discussed further

20. Loopback
 The 127.0.0.1 address, does not normally
exist on the network
– Either as the source address or destination
address of a packet
 The address is used internally by NICs
– When a NIC receives a message addressed with
127.0.0.1 to be transmitted, it passes the message
directly to the receiver hardware
– The receiver hardware returns the message to the
operating system exactly as if the message were
received from the network
• However, the message never entered the network
medium

21. Internal IP Addresses
 Depending on the address class needed by
an organization, a range of internal
addresses is available:
– Class A: 10.0.0.0 – 10.255.255.255
– Class B: 172.16.0.0 – 172.31.255.255
– Class C: 192.168.0.0 – 192.168.255.255
 IP routers outside a private (connection-
shared) network, will not forward datagrams
designated for addresses in these ranges

22. Multi-homed Machines
 There is no restriction preventing
machines from participating in multiple
networks
– A machine could have multiple NICs
– Each NIC would have its own MAC
address
– On TCP/IP networks, each of these NICs
would be given a different IP address

23. Routers
 Routers are multi-homed machines
– They have a number of network ports, each of
which represents a different path
 Routers use tables that relate destinations to
network paths
– Internet routers relate destination network
addresses with one of their network ports
– When a datagram arrives at a router:
• Its destination address is used to determine the network
address
• The network address is used to look up the destination
port in the routing table

24. Network Addresses
 An IP address can be used to calculate the
address of the network
 The machine address is passed through a
filter (called a subnet filter):
– This filter extracts the bits of the address that
represent the network and sets the bits that
represent the machine to zero
– The filter determines which part of the address
represent the network address, by using the
subnet mask

25. Subnet Mask
 The subnet mask is a binary number, that has
0s in the machine portion of the address, and
1s in the network portion
 Most networks of each type use a constant
subnet mask
– Class A: 255.0.0.0
(Binary: 11111111000000000000000000000000)
– Class B: 255.255.0.0
(Binary: 11111111111111110000000000000000)
– Class C: 255.255.255.0
(Binary: 11111111111111111111111100000000)

26. Using Subnet Masks
 Example:
– Address: 137.207.32.2
– Subnet Mask: 255.255.0.0
Address: 10001001110011110010000000000010
Mask: 11111111111111110000000000000000
Net Address: 10001001110011110000000000000000
 Network address: 137.207.0.0

27. IPv6
Next Generation Addressing
in TCP/IP Networks

28. IPv6
 Due to the limited nature of existing IP
addressing (IPv4), a new version of IP
addressing was developed
 This new scheme uses 16 octets for
addresses, instead of 4 octets
 Written using hex notation:
3A57:0000:0000:9CD5:3412:912D:6738:1928

29. IPv6 Features
 16 octet addresses (128 bits)
 Larger numbers of address classes
– More accurate control of network/machine counts
 Variable-sized headers
– Optional information can be placed into the header
when needed
– Reduces header size in most cases
 Extendible protocol
– IPv6 allows for new header information to be
added to support different protocols

30. IPv6 Features
 Automatically reconfigurable
– Addresses can be automatically reassigned
dynamically
– e.g. when a certain number of nodes join the
network, a different address class may be desired
 Autoconfigurable
– The use of autoconfiguration (such as DHCP)
allows dynamic private addressing and dynamic
public addressing

31. IPv6 Datagram Format
optional
header extension headers data

32. IPv6 Header Format
0 4 12 31
version traffic class flow label
32 48 56 63
payload length next header hop limit
64 96 128
source address destination address

33. IPv6 Integration
 Will IPv6 replace IP addresses?
– Who knows?
 Currently, temporary solutions have made
IPv4 addresses capable of lasting longer than
originally predicted
 If and when IPv6 is to be integrated, the
process must be a transition
– Closing the entire Internet down to convert
hardware and software to IPv6 not going to
happen
– Some stations may take longer to transition than
other stations
• e.g. Bob’s Internet Shack vs. the Telus Network

34. IPv6 Integration
 NAT (network address translators) provide one
example of such a temporary solution
 NATs provide three benefits:
1. NATs provide IP masquerading
• Messages using these addresses pass through a network
address translator (NAT) to be transformed into external IPs
2. NATs provide IP sharing
• ISPs for example, have many customers, but significantly
less at any given time are logged onto their system
– IP addresses can be assigned dynamically to these customers
when they log in
3. NATs provide schemes to allow networks to use either
IPv4 or IPv6
– Addresses would be converted as they pass through a NAT

35. IPv6 Integration
 Another method that may be used for the
transition between IPv4 and IPv6 is address
inclusion:
– IPv4 addresses could be embedded into IPv6
addresses
• Translation between the two types of addresses is
possible without any other information
– Some problems exist with this approach, but in
general it simplifies communication between
IPv6 networks and IPv4

36. Special IPv6 Addresses
 0:0:0:0:0:0:0:0 Used to indicate that this
machine is without an assigned IP
– Used during bootstrapping (e.g. requesting an IP
from a DHCP server)
 0:0:0:0:0:0:0:1 Used to send messages back
to this machine (called loopback)
– These two addresses are not valid on the actual
network medium (same as with IPv4)
 00:… Reserved (including IPv4 and IPX
address inclusion)
 FF:… Multicast addresses