Now that you're connected (Chapter 1), it's time to understand what networking really means and master the CLI like a professional network engineer. This chapter covers both network fundamentals and advanced CLI techniques.
A network is infrastructure that allows devices to communicate and share resources. Think of it as a combination of roads, postal system, and telephone network all in one.
Single building or campus. Example: office network, home network. Typically uses switches and WiFi access points.
Connects multiple LANs across cities/countries. Example: internet, corporate networks between offices. Uses routers and ISP connections.
City-wide network. Example: municipal WiFi, campus networks across a city.
Connects devices within the same network segment (LAN). Learns MAC addresses and forwards frames efficiently.
Maintains a MAC address table, learns source addresses, forwards to known destinations, floods unknown destinations.
VLAN support, Spanning Tree Protocol, Port security, Quality of Service (QoS)
Smart post office within a neighborhood - knows every house and delivers mail efficiently within the area.
Connects different networks together. Makes routing decisions based on IP addresses and routing tables.
Examines destination IP, consults routing table, forwards packets to next hop toward destination.
Static/Dynamic routing, NAT, DHCP, Access Control Lists, VPN termination
International postal service - determines best path to deliver mail between different countries/cities.
Provides wireless connectivity to wired network. Converts between wireless (802.11) and wired (Ethernet) protocols.
SSID management, WPA/WPA2 encryption, Band steering, Load balancing
Controls traffic flow based on security rules. Inspects and filters packets based on various criteria.
Stateful inspection, Application filtering, VPN support, Intrusion prevention
Basic monitoring and troubleshooting. Limited access for regular users.
ping, traceroute, telnet, ssh, basic show commands
View running config, change settings, access detailed information
Lowest - safe for non-technical users
Full monitoring capabilities, system maintenance, file operations
All show commands, copy, reload, debug, clear
Modify running configuration (read-only for configs)
High - full visibility, no modification
Device-wide configuration changes
hostname, interface, line, router, vlan, ip route
Entire device settings, global parameters
Maximum - can break network if misconfigured
Configure specific network interfaces/ports
ip address, switchport mode, speed, duplex, shutdown
Single interface only
Configure remote access (SSH, Telnet, Console)
password, login, transport input, exec-timeout
How users connect remotely
enableEnter Privileged EXEC mode. May prompt for password.
Shortcut: en
Reverse: disable
configure terminalEnter Global Configuration mode.
Shortcut: conf t
Alternative: config t
interface [type][number]Enter Interface Configuration mode.
Examples: int fa0/1, int gi1/0/1, int vlan1
line [type] [number]Enter Line Configuration mode.
Examples: line console 0, line vty 0 4
exitGo back one level in hierarchy.
Use: Step-by-step exit
endJump directly to Privileged EXEC mode.
Shortcut: Ctrl+Z
Use: Quick escape from any config mode
show versionHardware, software, uptime, memory info
Shortcut: sh ver
Shows: Model, IOS version, uptime, memory, configuration register
show running-configCurrent active configuration
Shortcut: sh run
Note: This is what's currently running (RAM)
show startup-configSaved configuration that loads at boot
Shortcut: sh start
Note: This is stored in NVRAM
show ip interface briefQuick interface status overview
Shortcut: sh ip int br
Shows: Interface, IP, Status, Protocol
show interfacesDetailed interface statistics
Shortcut: sh int
Shows: Errors, utilization, duplex, speed
show mac address-tableSwitch MAC address learning table
Shortcut: sh mac address-table
Shows: Learned MAC addresses per port
show cdp neighborsDirectly connected Cisco devices
Shortcut: sh cdp nei
Shows: Neighbor devices, their interfaces, platform
show ip routeRouting table (routers only)
Shortcut: sh ip route
Shows: All known networks and next hops
TabAuto-complete commands and parameters
Example: Type sho + Tab = show
?Context-sensitive help
Examples: ? (all commands), show ? (show options), interface ? (interface types)
command ?Show available parameters for command
Example: ip address ? shows IP address syntax
Navigate command history
Use: Recall and modify previous commands
show historyDisplay command history list
Shows: Last 10-20 commands (configurable)
Ctrl+A (beginning), Ctrl+E (end), Ctrl+U (delete line), Ctrl+K (delete to end)
| morePage through long output
Example: show running-config | more
| include [text]Show only lines containing specific text
Example: show run | include interface
| begin [text]Start output from first line containing text
Example: show run | begin vlan
| exclude [text]Hide lines containing specific text
Example: show int | exclude down
copy running-config startup-configSave current config to permanent storage
Shortcut: copy run start
Critical: Changes are lost without this!
reloadRestart the device
Note: Unsaved changes will be lost
write memoryAlternative way to save configuration
Same as: copy run start
An IP address is like a postal address for network devices. It has two main parts:
Identifies which "neighborhood" (network) the device belongs to
Identifies the specific "house" (device) within that neighborhood
IPv4 addresses are 32-bit numbers written as four octets separated by dots:
Use: Internal networks, not routed on internet
Use: Internet-facing services
Subnet mask determines which part of IP address is network vs host:
First 24 bits are network, last 8 bits are host
Example: In 192.168.1.100/24, network is 192.168.1.0
First 16 bits are network, last 16 bits are host
Example: In 172.16.5.100/16, network is 172.16.0.0
enable → Notice prompt change to #configure terminal → Notice (config)# promptinterface fastethernet 0/1 → Notice (config-if)# promptexit → Back to (config)#line console 0 → Notice (config-line)# promptend → Jump back to #? at each mode levelshow ? to see all show commandsinterface ? to see interface typesshow version → Record model and IOS versionshow running-config → Observe current settingsshow startup-config → Compare with running configshow ip interface brief → Note which interfaces are up/downshow interfaces → Check for errors or problemsshow mac address-table → See learned MAC addressesshow run | include interfaceshow int | exclude downsh run, sh ip int brshow history to see listshow running-config to verifycopy run start to save (or don't save for practice)❌ Making changes without copy run start
✅ Always save important changes immediately
❌ Trying configuration commands in EXEC mode
✅ Always check your prompt - know which mode you're in
❌ Pressing Enter without reading error output
✅ Read and understand every error message
❌ Guessing command syntax
✅ Use ? liberally to learn proper syntax
Professional engineers use sh run, not show running-config
Reduces typos and increases speed significantly
Up arrow and command editing saves massive amounts of time
Learn | include, | exclude, | begin for large configs
Use show run to capture "before" state, save configs with meaningful names
show commands, configuration management, troubleshooting1. You're in (config-if)# mode and need to check the running config. What's the fastest way? Press Ctrl+Z to jump to privileged mode, then sh run
2. What's the difference between running-config and startup-config? Running-config is active (RAM), startup-config is saved (NVRAM) and loads at boot
3. How do you see only interface-related lines in the running config? show run | include interface
4. What command shows you directly connected Cisco devices? show cdp neighbors (CDP = Cisco Discovery Protocol)
5. If 192.168.1.100/24 is the IP, what's the network address? 192.168.1.0 (the /24 means first 24 bits are network)
6. What happens to unsaved configuration changes if you reload? They're lost completely - always copy run start to save
7. How do you auto-complete a partially typed command? Press the Tab key after typing partial command
8. What's the shortcut to jump directly to privileged EXEC mode from any config mode? Ctrl+Z or end command
🎓 Excellent! You've mastered CLI navigation and network fundamentals. Ready to dive deep into IP addressing?
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