Perle Systems IOLINK-520 - Manual (Page 83)

IOLINK-520 & IOLINK-PRO Installation & Applications Guide — B.1
Appendix B
Octet Locations on
Ethernet Frames
This appendix provides octet locations for the various portions of three of the common
Ethernet frames. When creating pattern filters these diagrams will assist in the correct
definition of the patterns. The offset numbers are indicated by the numbers above the
frame representations.
Note the differences in the TCP/IP and Novell frames when bridging and when routing.
When routing, the TCP/IP and Novell frames are examined after the Level 2 Ethernet
portion of the frame has been stripped from the whole data frame. This means that the
offset numbers now start from 0 at the beginning of the routed frame and not the bridged
frame.
Some of the common Ethernet type codes are also shown here. The Ethernet type codes
are located at offset 12 of the bridged Ethernet frame.
Octet Locations on a Bridged TCP/IP Frame