Packet Captured Length Is Always 4 Less Than Packet Length

Hi All!!!

I noticed just now that on every one of my packets the Captured Length property is always 4 (bytes) less than Packet Length.

http://i144.photobucket.com/albums/r177/tackyjan/capsa-packetsize-offby4.png

Any ideas as to why this would be? Does this mean I am not getting all the data from the packet that was sniffed?

An interesting thing I noticed is that when I "decode" my packet (which contains a string message) the string is always chopped off by one character. For example, if I send the message "test1234" the data in the packet analyzer shows "test123".

Thanks!

 

Hi tackyjan,

This is a good question!

Packet Length = Captured Length + FCS Length. FCS length is 4 bytes, and Capsa will drop the FCS, so the captured length is 4 bytes shorter than the Packet length.

 

Yay! Thanks for the answer! Now I have to learn what FCS is.

 

I am guessing that the CS in FCS means checksum.