1. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Chapter 4 Network Layer

2. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Understand the position of the network layer in the Internet model. Understand the rationale for the existence of the network layer. Understand the concept of host-to-host delivery. Understand the duties of the network layer: packetizing, addressing, and routing. After reading this chapter, the reader should be able to: O BJECTIVES Know which upper-layer protocol can use the services of IP. Understand the network layer protocol, IP, used in the Internet.

3. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 INTRODUCTIONINTRODUCTION 4.1

4. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-1 Network layer in the Internet model

5. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-2 Duties of the network layer

6. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 ADDRESSINGADDRESSING 4.2

7. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 The network addresses must be unique. Note:

8. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Technical Focus: Binary Notation of IP Addresses An IP address is stored as a binary number in the computer. A 4-part dotted-decimal address can be converted to binary if we replace each part by its binary equivalent. The following shows the IP address 10.34.234.8 in dotted-decimal and binary notation: 10.34.224.8 00001010 00100010 11100000 00001000

9. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Technical Focus: Address Space A protocol such as IP that defines addresses has an address space. An address space is the total number of addresses available to the protocol. If a protocol uses N bits to define an address, the address space is 2 N because each bit can have two different values (0 and 1); N bits can have 2 N values. The Internet uses 32-bit addresses, which means that the address space is 2 32 or 4,294,967,296 (more than 4 billion). This means that theoretically, if there were no restrictions, more than 4 billion devices could be connected to the Internet.

10. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-3 Two levels of hierarchy

11. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 When using two levels of address hierarchy, the common part is referred to as the netid or prefix and the variable part is referred to as the hostid, or suffix. Note:

12. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-4 Three levels of hierarchy

13. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 With three levels of address hierarchy, the common part is referred to as the netid. The part common to all computers connected to the same subnet is referred to as the subnetid. The unique part is referred to as the hostid. Note:

14. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 A packet traveling from the source to the destination needs at least four addresses: source and destination port numbers and source and destination IP addresses. Note:

15. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-5 DNS example

16. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 ROUTINGROUTING 4.3

17. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-6 Example of portion of the Internet

18. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-7 Routing decisions

19. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-8 Routing table for router R1

20. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-9 Routing tables

21. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Routing tables can be based on next-hop routing. Note:

22. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Routing tables for the Internet are usually network-specific rather than host-specific. The router routes the packet to the final network; it is then broadcast to reach the final destination. Network-based routing reduces the size of routing tables. Note:

23. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-10 Autonomous systems

24. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Routing in the Internet is hierarchical. Delivery is first made to the autonomous system, then to the network, and finally to the host. Hierarchical routing reduces the size of the routing tables. Note:

25. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 PACKETIZING: IP PROTOCOL PACKETIZING: 4.4

26. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-11 Position of IP in Internet model

27. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Figure 4-12 IP datagram format

28. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Technical Focus: Fields in a Datagram The fields in a datagram are as follows: Version Header length Differentiated service Total length Identification, flags, and fragmentation offset Time to live Checksum Protocol Source address Destination address

29. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 FRAGMENTATIONFRAGMENTATION 4.5