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TCP/IP Analysis and Troubleshooting Toolkit phần 4

Là điểm đến của gói tin cho mạng cục bộ trên một mạng kết nối với router này?ARP cho địa chỉ MAC của các máy chủ địa phương, sau đó chuyển tiếp gói tin thông qua Layer 2 NO Là điểm đến của gói tin cho một mạng lưới không địa phương? | Inside the Internet Protocol 113 1 Packet arrives into a router interface 2 Is the destination of the packet a local IP address on this router 3 Is the destination of the packet for local network on a network connected to this router Action Look at the destination IP address in the packet YES Send the packet to the router operating system YES ARP for the MAC address of the local host then forward the packet via Layer 2 NO 4 YES Is the destination of the packet for a non-local network 5 Is there a default route Apply longest-match rule to find route for destination YES If a default route exists send the packet to the default router NO @ Drop the packet and send back a message informing user Figure 3-19 Route forwarding process. 114 Chapter 3 Case Study Local Routing When analyzing routing there are several important things to remember. The first is to know how traffic is being routed. You must see and verify the actual path that traffic is taking. The easiest routing problems to fix are ones where no traffic is being routed. In those cases you simply need to track down the router that isn t forwarding your packets. What happens though when communication is working although it s slow This example takes a look at a network where communications are working but performance is slow. The network used in this example is shown in Figure 3-20. It consisted of a flat Layer 2 network and one router that connected the organization to its parent corporation. When my team and I worked on this network our first order of business was to determine what kind of performance the users were getting. To do this we used our protocol analyzer to measure throughput during a file transfer. Because the users were all connected to the network via 100MB Fast Ethernet we expected to see throughput around 70-80Mbps per second. Figure 3-21 shows the results of our throughput analysis. 743 kilobytes per second was far from the 7 000-8 000 kilobytes per second we expected to see at 100MB network .