GSEC · Question #59
Regarding the UDP header below, what is the length in bytes of the UDP datagrarn? 04 1a 00 a1 00 55 db 51
The correct answer is D. 85. In the UDP header, bytes 4-5 contain the Length field, and 0x0055 converts to 85 decimal, representing the total datagram size in bytes.
Question
Regarding the UDP header below, what is the length in bytes of the UDP datagrarn? 04 1a 00 a1 00 55 db 51
Options
- A161
- B81
- C219
- D85
How the community answered
(29 responses)- A7% (2)
- B17% (5)
- C3% (1)
- D72% (21)
Why each option
In the UDP header, bytes 4-5 contain the Length field, and 0x0055 converts to 85 decimal, representing the total datagram size in bytes.
161 (0x00A1) is the value of the Destination Port field found in bytes 2-3, not the Length field.
81 (0x51) is the second byte of the Checksum field located at byte 7 of the header, not a length value.
219 (0xDB) is the first byte of the Checksum field at byte 6 of the header, not the Length field.
The UDP header is structured as four 2-byte fields: source port (bytes 0-1: 0x041A = 1050), destination port (bytes 2-3: 0x00A1 = 161), length (bytes 4-5: 0x0055 = 85), and checksum (bytes 6-7: 0xDB51). The Length field specifies the total size of the UDP datagram including the 8-byte header and payload. Converting 0x0055 from hexadecimal to decimal yields 85 bytes.
Concept tested: UDP header structure and length field parsing
Source: https://www.rfc-editor.org/rfc/rfc768
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