Why does tcpdump only capture the first 68 bytes of a packet?

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SUMMARY

TCPDUMP, by default, captures only the first 68 bytes of a packet to provide essential header information while maintaining user data privacy. This default setting is intentional, allowing for effective network diagnostics without compromising sensitive information. Users can modify this behavior by utilizing the "-s 0" option to capture the entire packet. Understanding this functionality is crucial for network administrators and security professionals.

PREREQUISITES
  • Familiarity with TCP/IP networking concepts
  • Basic knowledge of packet analysis tools
  • Understanding of network privacy and security protocols
  • Experience with command-line interfaces
NEXT STEPS
  • Explore TCPDUMP command-line options and usage
  • Learn about packet structure and headers in TCP/IP
  • Investigate network privacy implications of packet capturing
  • Study alternative packet analysis tools such as Wireshark
USEFUL FOR

Network administrators, cybersecurity professionals, and anyone involved in network diagnostics and packet analysis will benefit from this discussion.

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By default TCPDUMP limits the number of bytes it captures to 68. Why did they select 68 bytes? Does anyone know why?
 
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68 bytes is just the default value. You can set it to capture the whole packet by using the "-s 0" option. It's set to that by default because it's just enough to capture packet header information without revealing content; making it a useful network diagnostic without snooping through user data.
 

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