• Every device on ethernet needs a unique identifer called a ==MAC Address or Ethernet Address.==
    • MAC Address is 48 bits long, written as six pairs of colon-separated hexadecimal numbers. (23:34:00:3f:2b:12). Windows systems use dashes instead of colons.
    • First six numbers of the MAC adress identifies the Ethernet card manufacturer.
    • If the switch knows that the MAC address 52:54:00:3b:2b:25 is connected to switch port 87, ==it sends traffic for that MAC address exclusively to that port.==
  • Category 5, “cat5” cable, is the usual lowest common denominator these days. ==It has a maximum throughput of 100Mbs.==
  • A cat5e cable can handle gigabit speeds.
  • Datacenters might use cat6 cable, which can handle 10Gbps.
  • If you’re involved in the initial wiring of a new facility, you might consider cat7 cable, which can handle 40Gbs.

Speed & Duplex

  • Duplex refers to how each end handles transmitting and receiving data.

  • An interface running at half duplex can either receive or transmit data at any instance, but not both.

  • A full duplex connection can simultaneously send and receive.

  • Gigabit and faster Ethernet connections negotiate much more than speed and duplex, and autonegotiation is a mandatory part of the protocol.

    • Some network cards let the sysadmin hard-code gigabit speed and full duplex.