A few more notes to jog my memory:
Ethernet is 802.3 and includes wiring of some sort. Wireless LAN is 802.11 and is not Ethernet.
The Frame Check Sequence (FCS) is 4 bytes and is in the Ethernet trailer. It is used for error detection by computing a value and verifying it is the same when the frame is sent.
Ethernet standards:
802.3 = 10Base-T
802.3u = 100Base-T
802.3z = 1000Base-LX (max distance is 5000m)
802.3ab = 1000Base-T
802.3an = 10GBase-T
GBIC - Gigabit Interface Connector
SFP - Small Form-factor Pluggable module
Crossover cable connects pin 1 to pin 3 and pin 2 to pin 6.
Gb Crossover cable crosses pairs of wires, 1-2 go to 3-6, 4-5 go to 7-8
A data link header:
| Preamble | SFD | Src MAC | Dst MAC | Type | ---Data+padding--- | FCS |
| 7B | 1B | 6B | 6B | 2B | 1500B | 4B |
| -----------------Header-------------------| --- Payload ------| Trailer |
SFD - Start Frame Delimiter, signifies that the next sequence is the source MAC address.
A hub is a L1 device, repeats on all ports except the originating.
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