Ethernet header/trailer
nolaron
Registered Users Posts: 3 ■□□□□□□□□□
in CCNA & CCENT
When a computer receives a frame, does it get the header or trailer first? I always thought it received the header first but all of my material shows the frame being sent across the network with the trailer first (ie: sender |---[header][data][trailer]---> receiver).
When I think about it, I believe it needs the header first and the trailer last so it can do a proper FCS but I'm fuzzy on how the math works there. Does it need the payload to do the FCS or is that math done without the data being read yet? Sorry for asking such an elementary question but this is bugging me!!
When I think about it, I believe it needs the header first and the trailer last so it can do a proper FCS but I'm fuzzy on how the math works there. Does it need the payload to do the FCS or is that math done without the data being read yet? Sorry for asking such an elementary question but this is bugging me!!
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clarson
Member Posts: 903 ■■■■□□□□□□
The way we write things down is bit 1 is to the left, bit 2 is to the right of that, bit 3 is to the right of bit 2, etc. till the last bit is the furthest to the right.
But, bit 1 is sent first. and the last bit (which is shown the furthest to the right) is sent last.
the ethernet frame format starts with the preamble (shown to the left) and ends with the fcs (shown to the right). Every NIC out there is listening for the preamble. No preamble, They aren't listening for anything else till they receive that preamble (well at least as far as ethernet frames go).