1. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Network Layer: 19.1 Internetworks 19.2 Addressing Classful, Classless addressing, NAT 19.3 Routing

2. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.2 Links in an internetwork

3. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.3 Network layer in an internetwork

4. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.4 Network layer at the source

5. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 IP Packet Header bits

6. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.5 Network layer at a router

7. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Example A router inside the organization receives the same packet with destination address 190.240.33.91. Show how it finds the subnetwork address to route the packet. Solution The router follows three steps: 1.The router must know the mask. Assume it is /19. 2.The router applies the mask to the address, 190.240.33.91. The subnet address is 190.240.32.0. 3.The router looks in its routing table to find how to route the packet to this destination.

8. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Next-hop addressInterface 191.240.11.0 191.240.12.0 190.240.32.0 f1 f2 f3 191.240.12.0 190.240.32.0 191.240.11.0

9. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.6 Network layer at the destination

10. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.7 Switching

11. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.7 Switching

12. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.7 Switching

13. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.8 Datagram approach

14. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Switching at the network layer in the Internet is done using the datagram approach to packet switching. Note:

15. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Communication at the network layer in the Internet is connectionless. Note:

16. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 19.3 Routing Routing Techniques Static Versus Dynamic Routing Routing Table for Classful Addressing Routing Table for Classless Addressing

17. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Routing Techniques Next-hop routing Network-specific routing Host-specific routing Default routing

18. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.28 Next-hop routing

19. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.29 Network-specific routing

20. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.30 Host-specific routing

21. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.31 Default routing Network address 0.0.0.0

22. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Static and Dynamic Routing Tables Routes manually entered By administrator If Internet changes, table is updated manually Good for small internet, experiments, troubleshooting Routes periodically updated By protocols like RIP, OSPF, BGP (ch21) If Internet changes, protocols update tables. Good for big internet such as the Internet. StaticDynamic

23. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.32 Classful addressing routing table

24. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Example 10 Using the table in Figure 19.32, the router receives a packet for destination 192.16.7.1. For each row, the mask is applied to the destination address until a match with the destination address is found. In this example, the router sends the packet through interface m0 (host specific). 192.16.7.1 11000000 00010000 00000111 00000001 11111111 11111111 11000000 00010000 00000111 00000001 /32 192.16.7.1

25. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Example 11 Using the table in Figure 19.32, the router receives a packet for destination 193.14.5.22. For each row, the mask is applied to the destination address until a match with the next-hop address is found. In this example, the router sends the packet through interface m2 (network specific). 193.14.5.22 11000001 00001110 00000101 00010110 11111111 11111111 11111111 00000000 11000001 00001110 00000101 00000000 /24 193.14.5.0

26. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Example 12 Using the table in Figure 19.32, the router receives a packet for destination 200.34.12.34. For each row, the mask is applied to the destination address, but no match is found. In this example, the router sends the packet through the default interface m0. 200.34.12.34 11001000 00100010 00001100 00100010 00000000 00000000 /0 0.0.0.0

27. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Figure 19.32 Classless addressing routing table MaskDestination address Next-hop address Interface /24 … /24 /25 190.100.0.0 190.100.1.0 … 190.100.63.0 190.100.64.0 190.100.64.128 118.45.23.8 202.45.9.3 … 84.78.8.12 146.11.10.6 14.1.10.5 m0 m1 … m3 m0 m2

28. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 An example of address allocation and distribution by an ISP

29. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 No Hierarchical routing MaskDestination address Next-hop address Interface /24 /25 /24 /25 /24 /25 ABCDEFGHIJKLMOPQABCDEFGHIJKLMOPQ -BCBBBBBBCCCCCCC-BCBBBBBBCCCCCCCC - M0 M1 M0 M1

30. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Hierarchical routing (2-level) MaskDestination address Next-hop address Interface /24 /25 /24 A B C Region 2 Region 3 Region 4 Region 5 -BCBBCC-BCBBCC - M0 M1 M0 M1

31. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Geographic routing A U.S. backbone A European backbone Leased transatlantic lines Leased lines to Asia Regional network National network

32. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Summary Classful addressing (obsolete) Wasteful address archetecture Network boundaries are fixed at 8, 16 and 24 bits (class A, B, and C) Classless addressing Efficient address architecture Network boundaries may occur at any bit (/12, /16,/19,/24, etc) Best Current Practice

33. McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Summary NAT allows private network to use a set of private addresses internally, and global addresses externally. Routing Static / Dynamic Classful / Classless routing Hierarchical / Geographical routing Alleviates IP depletion Prevent immense routing table sizes Used for the Internet