power on self-test (POST)
First, the switch loads a power-on self-test (POST) program stored in ROM. POST checks the CPU subsystem. It tests the CPU, DRAM, and the portion of the flash device that makes up the flash file system.
boot loader
The boot loader performs low-level CPU initialization. It initializes the CPU registers, which control where physical memory is mapped, the quantity of memory, and its speed.
boot environment variable
In the figure, the BOOT environment variable is set using the boot system global configuration mode command.
boot system
show boot
mode button
system led
boot loader switch:
dir flash:
redundant power system (RPS) LED
port status LED
port duplex LED
port speed LED
power over ethernet (POE) LED
switch virtual interface (SVI)
VLAN
虛擬區域是一種建構於區域網路交換技術的網路管理的技術，網管人員可以藉此透過控制交換器有效分派出入區域網的封包到正確的出入埠，達到對不同實體區域網中的裝置進行邏輯分群管理，並降低區域網內大量資料流通時，因無用封包過多導致壅塞的問題，以及提昇區域網的資訊安全保障。
full-duplex
全雙工（full-duplex）的系統允許二台設備間同時進行雙向資料傳輸。 一般的電話、手機就是全雙工的系統，因為在講話時同時也可以聽到對方的聲音。 全雙工的系統可以用一般的雙向車道形容。 兩個方向的車輛因使用不同的車道，因此不會互相影響。
half-duplex
半雙工（half-duplex）的系統允許二台設備之間的雙向資料傳輸，但不能同時進行。 因此同一時間只允許一設備傳送資料，若另一設備要傳送資料，需等原來傳送資料的設備傳送完成後再處理。
auto-mdix
Using the automatic medium-dependent interface crossover (auto-MDIX)
feature on an interface eliminates this problem. When auto-MDIX is
enabled, the interface automatically detects the required cable
connection type (straight-through or crossover) and configures the
connection appropriately.
interface vlan 99
ip default-gateway
show ip interface brief
duplex auto
speed auto
mdix auto
show interfaces
input errors
runts
giants
CRC error
output errors
collisions
Collisions in half-duplex operations are normal. However, you should never see collisions on an interface configured for full-duplex communication.
late collisions
A late collision refers to a collision
that occurs after 512 bits of the frame have been transmitted. Excessive
cable lengths are the most common cause of late collisions.
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