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I've the following frame ethernet:
08 00 20 0A 70 66 08 00 20 0A AC 96 08 00 45 00 00 28 A6 F5 00 00 1A 06 75 94 C0 5D 02 01 84 E3 3D 05 00 15 0F 87 9C CB 7E 01 27 E3 EA 01 50 12 10 00 DF 3D 00 00 20 20 20 20 20 20 9B 52 46 43
Where 0x9B524643 is the FCS number. Using this tool (https://www.gasmi.net/hpd/) I can see that this FCS doesn't correspond to the real FCS that would be 0x5A05DEFA. How is the real FCS calculated (0x5A05DEFA)? Thanks

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1 Answer 1

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The FCS is a CRC over all fields (except the FCS) with the polynomial

G(x) = x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x + 1

with the procedure detailed in IEEE 802.3 Clause 3.2.9 - complement first 32 bits, run the polynomial, complement the result and transmit most significant to least significant bit - this is reverse the normal Ethernet order.

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  • Thanks for your answer. What does “complement” means? And what does “run the polynomial” means ?
    – DevShark
    Jan 26, 2020 at 15:32

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