tailieunhanh - practical packet analysis using wireshark to solve real world network problems phần 10

Khi ở chế độ màn hình, chạy lệnh iwconfig một lần nữa phản ánh những thay đổi của bạn. Bây giờ bảo đảm rằng giao diện eth1 là hoạt động bằng cách gõChúng tôi cũng sẽ sử dụng lệnh iwconfig để thực hiện quá trình nhảy kênh thảo luận trước đó trong chương này. | Once in monitor mode running the iwconfig command again should reflect your changes. Now ensure that the Eth1 interface is operational by typing iwconfig ethl up We ll also use the iwconfig command to perform the channel-hopping process discussed earlier in this chapter. Change the channel of the Eth1 interface by typing iwconfig ethl channel 3 NOTE You can do this on-the-fly as you are capturing packets so don t hesitate to change channels at will. This command can also be scripted using various Linux scripting languages to make the process easier. Once you have completed these configurations start Wireshark and begin your packet capture. Packet Extras 80211traffic The main difference between the packet structure of a wireless packet and pcap that of a standard packet is the addition of an header. This header contains extra information about the packet and the medium used to transmit it as shown in Figure 10-7. Figure 10-7 The header contains extra wireless information about the packets. To examine the packet shown in Figure 10-7 more closely open the example file. Let s look at some of the interesting items in this header Type Subtype This specifies the type or subtype of the packet shown. The type can be either management data or control. Each type can also have a subtype. For example the subtype of management packets can be beacon frame authentication request or disassociation notice. 142 Chapter 10 Destination Address Source Address and BSS Id These fields contain the source destination and BSS Id addresses of the packet. Fragment Number and Sequence Number These numbers are used to place the wireless packets in the appropriate order similar to the way TCP assembles data streams. Flags The header packet also contains a Flags section with even more wireless-specific information as shown in Figure 10-8. Figure 10-8 The Flags section contains more wireless-specific packet information. The Flags section .