Switches are devices that separate the environment into collision domains and operate at layer two. They ensure communication between devices in the network through MAC address tables (CAM tables) located on them. When you want to use a switch in a new network, it is necessary to erase the existing configuration on it. If the switch has not been used previously in a network, it will have no configuration.
Switches do not have power on/off buttons. The switch powers on immediately when connected to a power source. To perform the initial configuration of the switch, you need to connect to it via a console cable because the switch does not yet have an IP address accessible remotely.
Switches and routers provide information about the boot process through lights on them, called LEDs. Cisco switches have two system-related LEDs: system (SYST) and redundant power supply (RPS). Additionally, there is a mode button and associated LEDs to identify switch models.
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How does a switch work?
Among the functions of the switch are learning MAC addresses and storing them in the CAM table. The device retains learned MAC addresses for approximately 5 minutes. Using this information, it manages ports to direct traffic between devices.
At first startup, the switch’s memory is empty, and the CAM table contains no data. A computer connected to a port sends a frame containing source and destination MAC addresses. The device marks the port from which the frame came without yet knowing the destination port.
If the switch does not know the port to which it should send a frame, it broadcasts it to all ports except the one it came from. If no feedback is received, the MAC address is deleted from the table after 5 minutes.
A switch manages thousands of frames coming from each device. To do this efficiently, it uses ASIC (Application Integrated Circuitry) – specialized hardware chips that allow these functions to be performed at the hardware level.
The LEDs on the switch light green when everything is fine, orange when there is a problem, and during data transfer, the green LED blinks. During the boot process, the operating system is loaded from flash memory into RAM.
Initial Configuration Mode
When the switch starts for the first time, a text-based wizard appears. Usually, it is not used. When used, it offers three options:
- Skip to the IOS prompt without saving
- Return to the beginning of the initial configuration mode without saving
- Add this configuration to NVRAM
If we skip this mode, we reach the user exec mode.
User Exec Mode
In this mode, we can access information about the device’s operation but cannot see the current configuration. We can examine active routing protocols. From user exec mode, using the “enable” command, we can enter privileged exec mode.
Privileged Exec Mode
This is the mode where changes such as changing the time and date can be made, but without modifying the configuration. Changes made here are not saved in the configuration files. We can examine the entire device configuration. The person entering this mode has administrative rights.
Specific Configuration Mode
Changes made here affect only the specific section. All configurations are stored in RAM in the “Running Config.” To keep these changes permanent, they must be saved in the “Startup Config” file in NVRAM.
