1. 實驗四 Linux 子網域分割 之設定與觀察 教師： 助教：

2. 2 Outline Traditional IP Allocation Netmask: the Concept Subnetting Realization Proxy-ARP Transparent Router Different Lengths of Netmask How Kernel Works Broadcasting Routing Table Lookup Routing Table Cache Experiment

3. 3 Traditional IP Allocation

4. 4 Netmask: the Concept Used to determine whether two hosts are under the same network Unicast ： A → B A → Router → C Broadcast ： A → Everyone Router ： Longest Prefix Match

5. 5 Subnetting Realization - Proxy-ARP Transparent Router Get the mapping between MAC address and IP address of a host by ARP requests Sharing information with each subnet

6. 6 Subnetting Realization - Different Lengths of Netmask

7. 7 How Kernel Works Three possible scenarios when a packet arrives Routing Table Lookup, Routing Cache, Broadcasting Routing Table Lookup

8. 8 How kernel works Routing Cache Broadcasting Set destination Ethernet address to ff:ff:ff:ff:ff:ff

9. 9 Experiment Proxy-ARP B or C ping A B ping C Open ARP on A B or C ping A again B ping C again Longest Prefix Matching and Routing Cache Modify kernel source code and recompiled Load new kernel C ping B to check /var/log/messages Broadcasting