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The network layer supervises the handling of the packets by the underlying physical networks. We define this handling as the delivery of a packet. | 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 22.1 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 22.2 Route method versus next-hop method 22. Figure 22.3 Host-specific versus network-specific method 22. Figure 22.4 Default method . | 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 22.1 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 22.2 Route method versus next-hop method 22. Figure 22.3 Host-specific versus network-specific method 22. Figure 22.4 Default method 22. Figure 22.5 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 22.6. Example 22.1 Solution Table 22.1 shows the corresponding table. 22. Figure 22.6 Configuration for Example 22.1 22. Table 22.1 Routing table for router R1 in Figure 22.6 22. Show the forwarding process if a packet arrives at R1 in Figure 22.6 with the destination address 180.70.65.140. Example 22.2 Solution The router performs the following steps: 1. The first mask (/26) is applied to the destination address. The result is 180.70.65.128, which does not match the corresponding network address. 2. The second mask (/25) is applied to the destination address. The result is 180.70.65.128, which matches the corresponding network address. The next-hop address and the interface number m0 are passed to ARP for further processing. 22. Show
