Ethereal-users: [Ethereal-users] Packet Length calculation is odd ???

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From: David Moore <davem@xxxxxxxxx>
Date: Fri, 08 Jun 2001 16:51:26 -0400
I don't understand the packet length calculation. In a series of telnet session captures, Ethereal
indicates three back-to-back packets and their lengths as 1514, 1514, and 242.

The maximum ethernet packet including header is 1500 bytes. The difference between the packet
"Sequence number" and "Next sequence number" is 1460. This plus a standard 40 byte header is a full
1500 byte ethernet frame. So where does the 1514 come from ? This is 54 bytes too high not including
the header, or 14 bytes too high with the header.

Similarly the last packet indicates a length of 242 bytes. However, the sequence number difference
correctly show 188 bytes. Again there is a 54/14 byte error (depending on whether it's intended to
include the header).