I'm writing some code that produces PCAP-NG files that I subsequently read with
Wireshark. However, WS throws an error when I open the resulting file and it's
complaining about there not being enough data left in an Enhanced Packet Block
to satisfy the stated size of an option. I've think I know what's wrong but
it's led me to a fundamental question.
In the documentation in
https://www.winpcap.org/ntar/draft/PCAP-DumpFileFormat.html section 3.3 the
diagram shows that a variable length Options block can exist at the end of an
Enhanced Packet Block. I have assumed that if I don't want to specify options
I have to add an Option Code opt_endofopt and Option Length of zero at the
point, which comes to four bytes 0x00000000.
However, I've noticed that Wireshark generated traces don't seem to do this.
All the examples I have looked at have two bytes of zeros, but this happens to
align the end of the packet data on a 32-bit boundary and so I'm not sure if
that's the reason for the two bytes.
* If I don't want to add options to a packet, what should I add just
prior to the trailing Block Total Length value?
* Is this a Wireshark bug (writing incorrect format PCAP-NG files)?
Thanks and regards...Paul
Paul Offord FBCS CITP
Chief Technical Officer
Advance7
Phone: 01279 211 668
Mobile: 07764 931 431
Email: [email protected]<mailto:[email protected]>
LinkedIn: https://uk.linkedin.com/in/paulofford
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