tailieunhanh - Lecture Data communications and networking: Chapter 22 - Behrouz A. Forouzan

Chapter 22 - Network layer: Delivery, forwarding, and routing. This chapter describes the delivery, forwarding, and routing of IP packets to their final destinations. Delivery refers to the way a packet is handled by the underlying networks under the control of the network layer. Forwarding refers to the way a packet is delivered to the next station. Routing refers to the way routing tables are created to help in forwarding. | Chapter 22 Network Layer: Delivery, Forwarding, and Routing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22. 22-1 DELIVERY The network layer supervises the handling of the packets by the underlying physical networks. We define this handling as the delivery of a packet. Direct Versus Indirect Delivery Topics discussed in this section: 22. Figure Direct and indirect delivery 22. 22-2 FORWARDING Forwarding means to place the packet in its route to its destination. Forwarding requires a host or a router to have a routing table. When a host has a packet to send or when a router has received a packet to be forwarded, it looks at this table to find the route to the final destination. Forwarding Techniques Forwarding Process Routing Table Topics discussed in this section: 22. Figure Route method versus next-hop method 22. Figure Host-specific versus network-specific method 22. Figure Default method 22. Figure Simplified forwarding module in classless address 22. In classless addressing, we need at least four columns in a routing table. Note 22. Make a routing table for router R1, using the configuration in Figure . Example Solution Table shows the corresponding table. 22. Figure Configuration for Example 22. Table Routing table for router R1 in Figure 22. Show the forwarding process if a packet arrives at R1 in Figure with the destination address . Example Solution The router performs the following steps: 1. The first mask (/26) is applied to the destination address. The result is , which does not match the corresponding network address. 2. The second mask (/25) is applied to the destination address. The result is , which matches the corresponding network address. The next-hop address and the interface number m0 are passed to ARP for further processing. 22. Show | Chapter 22 Network Layer: Delivery, Forwarding, and Routing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22. 22-1 DELIVERY The network layer supervises the handling of the packets by the underlying physical networks. We define this handling as the delivery of a packet. Direct Versus Indirect Delivery Topics discussed in this section: 22. Figure Direct and indirect delivery 22. 22-2 FORWARDING Forwarding means to place the packet in its route to its destination. Forwarding requires a host or a router to have a routing table. When a host has a packet to send or when a router has received a packet to be forwarded, it looks at this table to find the route to the final destination. Forwarding Techniques Forwarding Process Routing Table Topics discussed in this section: 22. Figure Route method versus next-hop method 22. Figure Host-specific versus network-specific method 22. Figure Default method .