Introduction
Before a switch or end device can participate properly in a network, it needs basic settings such as a device name, secure access, IP addressing information, and a default gateway. Network technicians often configure these settings through a command-line interface.
Operating System Components
An operating system provides the interface between users, software, and hardware.
| Component | Role |
|---|---|
| Shell | Accepts user commands through a graphical interface or command line. |
| Kernel | Manages hardware resources and coordinates software requests. |
| Hardware | The physical parts of the device. |
A GUI uses windows, icons, menus, and pointers. A CLI uses typed commands. Network devices commonly use CLI access because it is efficient, scriptable, and available even when a graphical interface is not.
Cisco IOS Access Methods
Common access methods for a Cisco IOS device include:
| Method | Use |
|---|---|
| Console | Direct physical access, often used for initial setup or recovery. |
| SSH | Secure remote CLI access over the network. |
| Telnet | Remote CLI access without encryption; generally avoided because commands and passwords are sent in readable form. |
Terminal emulation tools allow a technician to connect through console, SSH, or Telnet sessions.
IOS Navigation
Cisco IOS uses different command modes. Each mode controls what commands are available.
| Mode | Example Prompt | Purpose |
|---|---|---|
| User EXEC | Switch> | Basic monitoring commands. |
| Privileged EXEC | Switch# | More powerful verification and management commands. |
| Global configuration | Switch(config)# | Device-wide configuration. |
| Subconfiguration modes | Switch(config-if)#, Switch(config-line)# | Interface, line, or other specific settings. |
A technician enters privileged EXEC mode with enable, then enters configuration mode with configure terminal.
Command Structure and Help
IOS commands usually begin with a keyword and may include required or optional arguments. The CLI supports features that help avoid mistakes:
?displays available commands or parameters.Tabcompletes a partial command when the entry is unique.- Arrow keys recall or edit commands.
Ctrl+Cexits many configuration operations.endreturns to privileged EXEC mode.
When output is long, IOS may pause with a --More-- prompt so the technician can continue reading one screen at a time.
Basic Device Configuration
A basic switch setup usually includes a hostname, protected privileged EXEC access, console access security, remote access security, password encryption, and a login warning banner.
Passwords should be strong and should not be easy to guess. Remote access should use SSH instead of Telnet whenever possible.
Basic Switch Configuration Lab
Saving Configurations
Cisco IOS keeps active settings in the running configuration. These settings are lost after a reboot unless they are saved. The saved version is called the startup configuration.
Important commands:
show running-config
show startup-config
copy running-config startup-config
erase startup-config
reload
Use saving commands carefully. Erasing or reloading a device can interrupt network service.
Ports, Interfaces, and Addresses
A switch has physical ports that connect to end devices and other network devices. A Layer 2 switch can still have an IP address for management. This IP address is usually configured on a Switch Virtual Interface (SVI), commonly VLAN 1 in simple labs.
End devices need the following IP settings:
- IP address
- Subnet mask or prefix length
- Default gateway
- DNS server address, when name resolution is needed
The default gateway is the router interface a host uses to send traffic outside its local network.