Basic Device Configuration

Network devices should be configured in a predictable and secure way before they are placed into production. This module focuses on the first tasks usually performed on Cisco switches and routers: preparing a switch for management, configuring switch ports, enabling secure remote access, setting up basic router interfaces, and verifying that directly connected networks can communicate.

By the end of this module, you should be able to:

• Explain the basic boot process of a Cisco switch.
• Configure a switch management interface and default gateway.
• Set switch port speed, duplex, and auto-MDIX behavior.
• Use verification commands to inspect switch and router status.
• Prefer SSH over Telnet for remote administration.
• Configure basic IPv4 and IPv6 settings on router interfaces.
• Verify directly connected routes and interface status.

When a Cisco switch powers on, it performs several startup steps before the operating system becomes available:

1. POST runs from ROM. The power-on self-test checks key hardware such as the CPU, memory, and flash file system.
2. The boot loader starts. This small ROM-based program runs after POST completes successfully.
3. Low-level CPU settings are initialized. The boot loader prepares memory mapping and basic CPU operation.
4. Flash storage is prepared. The switch initializes the flash file system where the operating system image and configuration files are stored.
5. IOS is loaded. The boot loader finds an IOS image, loads it into memory, and passes control to IOS.

The switch can use a configured boot variable to determine which IOS image to load. If no boot variable is set, it normally attempts to boot from the first valid executable image it finds in flash.

Switch LEDs provide quick physical clues about device status. Common indicators include:

• SYST: Shows whether the switch has power and is operating normally.
• RPS: Indicates redundant power supply status if supported.
• STAT: Shows port link/activity status.
• DUPLX: Shows whether a port is using half-duplex or full-duplex.
• SPEED: Shows the link speed for each port.
• PoE: Shows Power over Ethernet status if the switch supports it.

The mode button changes what port LEDs represent. For example, in STAT mode a solid green port LED usually indicates link up, while a blinking green LED commonly represents traffic activity. Amber or alternating colors usually indicate a blocked port, fault, or power-related issue.

If IOS cannot load because system files are missing or damaged, the boot loader can be used for recovery. A console connection is required. The common recovery idea is:

1. Connect to the switch using a console cable and terminal software.
2. Power-cycle the switch.
3. Hold the mode button during startup until the boot loader prompt appears.
4. Use boot loader commands to inspect flash, recover passwords, format storage, or reinstall IOS.

Useful boot loader commands include directory inspection commands such as dir.

A Layer 2 switch does not need an IP address to forward Ethernet frames, but it does need one for remote management. Management access is normally configured through a Switch Virtual Interface (SVI).

An SVI is a logical VLAN interface, not a physical port. The management SVI should have:

• an IPv4 address and subnet mask,
• optionally an IPv6 address,
• the interface enabled with no shutdown,
• a default gateway if the administrator will connect from another network.

For better security, avoid using VLAN 1 as the management VLAN when possible.

A switch port can operate in half-duplex or full-duplex mode.

• Full-duplex allows sending and receiving at the same time. It is more efficient and eliminates collisions on that link.
• Half-duplex allows only one direction at a time. It can experience collisions and lower performance.

Modern wired Ethernet networks should use full-duplex whenever possible. Gigabit and faster Ethernet links normally operate in full-duplex mode.

Switch ports can use automatic negotiation or manual settings. Autonegotiation is useful when the connected device may vary, while manual configuration is common for known infrastructure devices such as servers, routers, and uplinks.

Auto-MDIX allows the switch to automatically handle straight-through or crossover cable requirements. On devices that support it, the port can adjust to the cable type automatically. Auto-MDIX works best when speed and duplex are set to auto.

Use show commands to confirm configuration and troubleshoot problems.

The first line of show interfaces is important. For example:

FastEthernet0/18 is up, line protocol is up

The first status describes the physical layer. The second describes the data link layer.

• up/up: The interface is physically connected and the data link protocol is working.
• up/down: The cable signal may exist, but the data link layer has a problem. Possible causes include encapsulation mismatch, remote error-disable state, or hardware issues.
• down/down: The port is not detecting a working physical connection. Check cable, remote device, and speed settings.
• administratively down: The interface was disabled with the shutdown command.

Interface counters help identify performance problems even when the link is technically up.

Telnet uses TCP port 23 and sends usernames, passwords, and session data in plaintext. Because anyone capturing traffic can read the login details, Telnet should not be used for production device management.

SSH uses TCP port 22 and encrypts the management session. It protects both authentication and command traffic. For network administration, SSH should be the standard remote access method.

A router forwards traffic between different networks. At minimum, a router should have:

• a hostname,
• secure privileged access,
• encrypted passwords where possible,
• configured and enabled interfaces,
• saved configuration,
• verification that directly connected networks appear in the routing table.

A loopback interface is a logical router interface that stays up as long as the router is running. It is useful for testing, management, routing protocol identification, and stable reachability.

After router interfaces are configured, use verification commands to check status and routes.

A directly connected route normally appears when the interface has an address, the interface is up, and the line protocol is up.