cheat sheet Flashcards
(25 cards)
layer 7
Name
Function
Data Unit
Devices Protocols/Examples
Application
User interface, network services Data Application software HTTP, FTP, SMTP, DNS
layer 6
Name
Function
Data Unit
Devices Protocols/Examples
6
Presentation
Data format, encryption, compression Data — JPEG, SSL/TLS, MPEG
layer 5
Name
Function
Data Unit
Devices Protocols/Examples
5 Session Session management (open, maintain, close) Data — NetBIOS, RPC
layer 4
Name
Function
Data Unit
Devices Protocols/Examples
4 Transport Reliable delivery, flow control, ports Segment — TCP, UDP
layer 3
Name
Function
Data Unit
Devices Protocols/Examples
3 Network Routing, logical addressing (IP) Packet Router IP, ICMP, OSPF
layer 2
Name
Function
Data Unit
Devices Protocols/Examples
2 Data Link MAC addressing, local delivery Frame Switch, Bridge, NIC Ethernet, PPP, AR
layer 1
Name
Function
Data Unit
Devices Protocols/Examples
1 Physical Transmit bits over media Bits Hub, Cable, Repeater Fiber, RJ45, Wireless, DSL
Encapsulation Order (Sending Data)
Application → Transport → Network → Data Link → Physical
App generates data
Transport adds port info (TCP/UDP segment)
Network adds IP address (packet)
Data Link adds MAC address (frame)
Physical sends bits over wire
Decapsulation Order (Receiving Data)
Physical → Data Link → Network → Transport → Application
TCP vs. UDP at Layer 4
Feature TCP UDP
Connection Yes (3-way handshake) No
Reliability Reliable, ordered Unreliable, unordered
Speed Slower Faster
Use Case Web, Email, File Transfer Streaming, DNS, VoIP
Devices at Each Layer
Layer Devices
1 Hub, Cable, Repeater
2 Switch, Bridge, NIC
3 Router
4–7 Software (firewalls, apps, OS services)
Common Protocols Per Layer
Layer Protocols/Examples
7 HTTP, FTP, SMTP, DNS
6 SSL, TLS, JPEG, ASCII
5 NetBIOS, RPC
4 TCP, UDP
3 IP, ICMP, OSPF, EIGRP
2 Ethernet, ARP, PPP
1 Wi-Fi, Fiber, DSL, Coax, RJ45
What is Cisco IOS?
Cisco IOS stands for Internetwork Operating System.
It is the software that runs on Cisco routers and switches.
Allows users to configure, monitor, and troubleshoot network devices using a Command Line Interface (CLI).
IOS is stored in Flash memory, loaded into RAM when the device boots.
Ways to Connect to a Cisco Device with console, ssh, telnet, aux
Connection Type Description When It’s Used
Console Direct cable connection to the device First-time setup
SSH Secure remote connection over a network Preferred for remote access
Telnet Unsecure remote access (clear-text) Legacy or test environments
AUX Access via modem connection Rarely used today
IOS User Modes and Prompts:
User EXEC mode
Privileged EXEC
Mode Name:
Prompt Example:
What You Can Do:
How to Enter:
User EXEC mode
Router>
Basic checks, limited commands Just press Enter
🔑 Use exit to go back one level, and end or Ctrl+Z to return to EXEC mode.
IOS User Modes and Prompts:
Privileged EXEC
Mode Name:
Prompt Example:
What You Can Do:
How to Enter:
Router#
All “show” commands, debug, etc. Type enable
🔑 Use exit to go back one level, and end or Ctrl+Z to return to EXEC mode.
IOS User Modes and Prompts:
Global Configuration
Mode Name:
Prompt Example:
What You Can Do:
How to Enter:
Router(config)#
Make system-wide config changes configure terminal
🔑 Use exit to go back one level, and end or Ctrl+Z to return to EXEC mode.
IOS User Modes and Prompts:
Interface Configuration
Mode Name:
Prompt Example:
What You Can Do:
How to Enter:
Router(config-if)#
Configure an interface
interface Gig0/0 (for example)
🔑 Use exit to go back one level, and end or Ctrl+Z to return to EXEC mode.
Basic Navigation & Help Commands
enable
disable
configure terminal
exit
end or Ctrl+Z
show ?
show running-config
show startup-config
Command What It Does
enable Enter Privileged EXEC mode
disable Return to User EXEC mode
configure terminal Enter Global Config mode
exit Exit the current mode
end or Ctrl+Z Exit to EXEC mode
show ? See available commands
show running-config Show current (active) settings
show startup-config Show saved config (in NVRAM)
🧠 Tip: Use the Tab key to auto-complete commands. For example: conf t → configure terminal.
how to Manage Configurations?
Running Configuration
Startup Configuration
Running Configuration Temporary config stored in RAM. Lost when the device is rebooted.
Startup Configuration Saved config stored in NVRAM. Loaded when the device restarts.
To save configuration permanently, use:
copy running-config startup-config
To erase saved configuration (startup):
erase startup-config
To reboot the device after erasing:
reload
File System & Memory Terms of ios:Flash,NVRAM,RAM,ROM
Flash – Stores the IOS image file.
NVRAM – Stores the startup configuration.
RAM – Used for running configuration and buffers.
ROM – Contains bootstrap program & ROMMON mode.
