Switch startup and verification

Four memory types

• RAM (volatile): the running config. The startup config is copied here at boot.
• NVRAM (non-volatile): the startup config.
• ROM (non-volatile): bootstrap code, POST microcode, the ROM monitor.
• Flash (non-volatile): the IOS image, optionally config backups. Think hard drive.

No startup config in NVRAM means the switch drops into the setup utility with a default config. The instructor’s advice: decline the initial configuration dialog, the wizard is long and unhelpful; configure from the CLI instead.

ROM monitor (ROMMON) is a low-level OS used for manufacturing, testing, troubleshooting, and password recovery.

Running config changes live only in RAM until copied to startup config. Details in config files.

Console access

No keyboard or monitor on a switch: first-time config happens over the console port from a PC.

Ports: the traditional RJ-45 serial console, with newer devices adding USB (mini-B or USB-C). With both present, only one is active: plugging into USB deactivates RJ-45, unplugging hands it back.

The cable depends on what your laptop has: RJ-45-to-DB-9, USB-A adapters, mini-B, or USB-C-to-RJ-45 variants. Modern laptops almost always need some USB flavor.

Terminal emulator settings (Tera Term, PuTTY, and friends): 9600 bps, 8 data bits, no parity, 1 stop bit, no flow control.

A console connection lands you in user EXEC mode.

Physical install and boot

Verify power and environment first (temperature, humidity), then rack, wall, or shelf mount, then check cabling to end devices (SFPs between switches, Cat 5/6 to hosts).

Many Catalysts have no power button: plugging in the AC cord boots them. So connect the console cable and open the terminal program before plugging in, or you miss the boot output. Seat the power connector fully.

At boot, POST runs (LEDs blink through the self-tests), then IOS loads and its output scrolls on the console.

Reading the LEDs

Green is normal and amber is trouble, as a general rule. The mode button cycles what the per-port LEDs mean (status, speed, duplex, active, stack, PoE).

• System: off = no power. Green = IOS loaded and operational. Blinking green = loading software. Amber = POST failed and IOS did not load.
• Status (per port): green = link but idle, blinking green = traffic, amber = port blocked.
• Duplex (per port): on = full duplex, off = half.
• Speed (per port): off = 10 Mbps, solid green = 100 Mbps, one flash = 1 Gbps, two flashes = faster than 1 Gbps.
• Stack: which member number this switch is in a stack.
• Active: green = active or standalone, slow blink = stack standby.
• PoE: per port, whether it’s supplying power.
• XPS / S-PWR: expandable power system / StackPower cabling status.
• Console: which console port is active (off = USB console disabled).

The System LED alone answers the first troubleshooting question: dead (off), healthy (green), or failed POST (amber).

show interfaces

SwitchX# show interfaces FastEthernet 0/1
FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 001e.147c.bd01 (bia 001e.147c.bd01)
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
  ...
  Full-duplex, 100Mb/s, media type is 10/100BaseTX
  5 minute input rate 31000 bits/sec, 33 packets/sec
  0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

The first status is hardware, Layer 1 (up means not shut down and physically alive). The second is line protocol, Layer 2. “up/up” means the interface can move frames, and hardware down forces line protocol down too.

Also shown: the port’s own MAC, encapsulation, duplex and speed, traffic rates, and error counters. CRC and input errors climbing means suspect the cable (length, interference). Counters can be cleared to watch fresh.

show version

IOS version and image filename (report the full version string when raising bugs), uptime, hardware model and RAM, processor board ID (the serial number), interface counts.

At the bottom of the output sits the configuration register, which controls how the device boots (normal, ignore startup config, and so on). Changing it is part of password recovery.

Works the same on routers. See duplex notes for the related interface checks.

show running-config

The live config in RAM. Two timestamps at the top tell a story:

! Last configuration change at 08:51:52 UTC Wed Aug 22 2012
! NVRAM config last updated at 06:26:14 UTC Wed Aug 22 2012

If those drift apart, there are unsaved changes. Two weeks apart means two weeks of edits nobody copied to startup config.

Management IP on a Layer 2 switch

interface Vlan1
 ip address 172.20.137.5 255.255.255.0
!
ip default-gateway 172.20.137.1

A plain Layer 2 switch gets its management address on an SVI (interface VLAN 1 traditionally). That’s the address you SSH to or ping.

ip default-gateway points management traffic off-subnet, the same job as the gateway setting on any host. Without it, an admin on another subnet can’t reach the switch.