Wireshark · Wireshark-dev: Re: [Wireshark-dev] need to read three bytes of offset

[prashanth joshi <prashanthsjoshi2000@xxxxxxxxx>]

Thanks Harris for the response. In our case the functional spec of the company says that the offset is a three byte field. And I am reading the packets from the pcap captured on wireshark / tcpdump.

 

Regards,

Prashanth

--- On Thu, 3/4/10, Guy Harris <guy@xxxxxxxxxxxx> wrote:

From: Guy Harris <guy@xxxxxxxxxxxx>
Subject: Re: [Wireshark-dev] need to read three bytes of offset
To: "Developer support list for Wireshark" <wireshark-dev@xxxxxxxxxxxxx>
Date: Thursday, March 4, 2010, 12:01 PM

On Mar 4, 2010, at 7:23 AM, prashanth s wrote:

> I am reading a pcap file and writing to a text file. I am getting a field offset which is supposed to be of three bytes long. How do I read it?
> Should I assume that the three bytes obey the network byte order or are the three bytes of offset are supposed be just read as three bytes of u_char type?

There are no 3-byte fields in the pcap per-packet header, so you must be referring to a field in a packet.

Whether they're a 3-byte integral value in network byte order (big-endian byte order), a 3-byte value in little-endian byte order, 3 one-byte values, a 2-byte integral value in network byte order followed by a 1-byte value, a 2-byte integral value in little-endian byte order followed by a 1-byte value, a 1-byte value followed by a 2-byte value in network byte order, a 1-byte value followed by a 2-byte value in little-endian byte order, etc. is indicated by the specification for the protocol to which that field belongs.
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