Wireshark Lab : UDP v7.0

Wireshark_UDP_v7.0.pdf

1. Select one UDP packet from your trace. From this packet, determine how many fields there are in the UDP header. (You shouldn’t look in the textbook! Answer these questions directly from what you observe in the packet trace.) Name these fields.

>> UDP header는 4개의 필드를 포함하고 있다. Source Port, Destination Port, Length, Checksum.

2. By consulting the displayed information in Wireshark’s packet content field for this packet, determine the length (in bytes) of each of the UDP header fields.

>> 2 Byte의 필드 4개가 있으므로, 총 8 Byte다.

Source Port : 2 Byte

Destination : 2 Byte

Length : 2 Byte

Checksum : 2 Byte

3. The value in the Length field is the length of what? (You can consult the text for this answer). Verify your claim with your captured UDP packet.

>> Length field의 값은 8개의 header Byte와 packet에 캡슐화 된 나머지 data Byte의 합이다.

4. What is the maximum number of bytes that can be included in a UDP payload? (Hint: the answer to this question can be determined by your answer to 2. above)

>> payload에 포함될 수 있는 최대 바이트는 2¹⁶(2^16) – header field에서 이미 사용 중인 바이트(8Byte)다. 즉, 최대 UDP payload는 65535 – 8 = 65527Byte다.

5. What is the largest possible source port number? (Hint: see the hint in 4.)

>> 가능한 최대 source port number는 2¹⁶(2^16) or 65535다.

6. What is the protocol number for UDP? Give your answer in both hexadecimal and decimal notation. To answer this question, you’ll need to look into the Protocol field of the IP datagram containing this UDP segment (see Figure 4.13 in the text, and the discussion of IP header fields).

>> decimal(10진수) : 17 | hexadecimal(16진수) : 11(0x11)

7. Examine a pair of UDP packets in which your host sends the first UDP packet and the second UDP packet is a reply to this first UDP packet. (Hint: for a second packet to be sent in response to a first packet, the sender of the first packet should be the destination of the second packet). Describe the relationship between the port numbers in the two packets.