1. Network Layer, and Logical Addresses
Chapter 18
COMP 3270 Computer Networks
Computing Science
Thompson Rivers University

2. Host-to-host delivery of packets
Network Layer
☺ Main responsibility?
Host-to-host delivery of packets

3. Position of the network layer
Sour port number
Source address
Source & destination port number
Logical destination address
TCP, UDP
IGMP
Source address
Logical destination address IP
ARP
RIP, OSPF
Physical destination address
Interface
Ethernet, Token ring, W-LAN, FDDI, …

4. Network layer duties A view of a global Routing and Network over many
different physical
networks
Routing and
forwarding
Globally unique
addressing scheme

5. 1. INTERNETWORKING Topics discussed in this section:
In this section, we discuss internetworking, connecting networks together to make an internetwork or an internet.
☺ What is an internetwork?
Review of the IP packet forwarding mechanism.
Topics discussed in this section:
Need for Network Layer
Internet as a Datagram Network
Internet as a Connectionless Network

6. ☺ How do A and D exchange data?
Need for Network Layer
Links between two hosts
LAN
☺ How do A and D exchange data?

7. Host-to-host delivery
Each data link handles its own network interface only;
There is no interaction between them even though they are in the same switch system S1.
Host-to-host delivery
☺ How to decide the next hop for the traffic from A to D, through f2 or f3?
LAN
Data link layer;
Physical layer

8. S1 is connected to S3 through f3.
It decides the next hop
(the IP address of S3 and the interface f3) f1 f3 f1 f2
LAN

9. Internet as a Datagram Network
The datagram approach to packet switching, and connectionless service.
Telecommunications networks
ATM, FR, X.25
The Internet

10. There is no specific route established from the source to the destination.
They can arrive in a different order;
Reordering does not occur
in the network layer.
☺ Then in which layer?

11. ☺ How many different types of address are used in the Internet 5 layers?

12. 4. IPv4 ADDRESSES Topics discussed in this section:
An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a device (for example, a computer or a router) to the Internet.
Topics discussed in this section:
Address Space
Notations
Classful Addressing
DHCP

13. Address Space An IPv4 address is 32 bits long.
The address space of IPv4 is 232 or 4,294,967,296.
The public IPv4 addresses are unique and universal.

14. Notations

15. Dotted-decimal notation & binary notation

16. Example:
Change the following IPv4 addresses from binary notation to dotted-decimal notation.
Solution:

17. Example:
Change the following IPv4 addresses from dotted-decimal notation to binary notation.
Solution:

18. Example:
Find the error, if any, in the following IPv4 addresses.

19. Addressing
An IP address consists of Netid (or also called address block id) + Hostid.
A netid represent a logical IP network.
Two addressing schemes.
classful addressing
classless addressing

20. Classful Addressing
In classful addressing, the address space is divided into five classes:
A, B, C, D, and E.

21. Finding the classes in binary and dotted-decimal notation
An IP address consists of Netid + Hostid.
A netid represent a logical IP network.
☺ How to get the netid to which an IP address belongs?

22. Example: Find the class of each address.b c d

23. Number of blocks and block size in classful IPv4 addressing
3 bytes
In classful addressing, classful address blocks are allocated to IP networks (logical networks), and a large part of the available addresses were wasted.

24. Default netmasks for classful addressing
☺ Given an address, how to find the address block to which
the address belongs ???
☺ IP address BIT_AND netmask = ???
E.g., & =
/24 represents the address block of
addresses from to

25. Classless Addressing
In classless addressing, the netids do not have to use 1B, 2B, or 3B.
Any number of bits can be used for netids.
☺ How?
/n and netmask
Classless addressing is used in IP packet forwarding and routing.

26. DHCP (Dynamic Host Configuration Protocol)
DHCP provides static and dynamic address allocation that can be manual or automatic.
☺ DHCP server must be in the same physical network?
☺ There could be two DHCP servers
in the same physical network?
☺ What information is assigned by DHCP?

27. An IPv6 address is 128 bits long.
IPv6 ADDRESSES
IPv6 is a next generation IP.
Despite all short-term solutions, address depletion is still a long-term problem for the IPv4 Internet. This and other problems in the IPv4 protocol itself have been the motivation for IPv6.
An IPv6 address is 128 bits long.