Networking 2 Reviewer - OSI, TCP/IP, and Cisco Commands

Open Systems Interconnection (OSI) Model:
- Definition: Explains how devices communicate over a network.
- Structure: Consists of $7$ layers.
- Mnemonic (Layer 7 to Layer 1): A P S T N D P — "All People Seem To Need Data Processing".
- Common Protocols and Functions:
  - HTTP / HTTPS: Websites
  - FTP: File transfer
  - SMTP: Email
  - DNS: Finds names / IP addresses
  - SSH: Secure remote access
TCP/IP Model (Transmission Control Protocol & Internet Protocol):
- Structure: Consists of $4$ layers:
  - Application
  - Transport
  - Internet
  - Network Access / Link

Layer 7: Application:
- Easy Meaning: Apps use the network.
- Function: This is where network applications and services are used.
Layer 6: Presentation:
- Easy Meaning: Changes / formats the data.
- Function: Makes sure the data is in a form the other device can understand (Data format).
- Operations Handled:
  - Formatting
  - Translation
  - Encoding
  - Compression
  - Encryption / Decryption
Layer 5: Session:
- Easy Meaning: Starts and ends communication.
- Function: Manages the conversation or session between applications.
- Operations Handled:
  - Starts communication
  - Maintains communication
  - Synchronizes communication
  - Ends communication
Layer 4: Transport:
- Easy Meaning: Delivers data.
- Function: Makes sure data gets from one application to another.
- Protocols:
  - TCP (Transmission Control Protocol): Reliable (Careful)
  - UDP (User Datagram Protocol): Fast & Simple
Layer 3: Network:
- Easy Meaning: Finds the route.
- Function: Decides "Where should the data go?" (Network = IP + Routing).
- Operations Handled:
  - IP addresses
  - Routing
  - Packet forwarding
  - Choosing paths
Layer 2: Data Link:
- Easy Meaning: Uses MAC address.
- Function: Handles communication between devices on the same local network (Data Link = MAC + Frame).
- Identifier Used: MAC addresses
Layer 1: Physical:
- Easy Meaning: Sends bits.
- Function: The actual physical transmission of data.
- Unit Sent: Bits

IPv4 (Internet Protocol Version 4):
- Address Length: Uses $32\text{-bit}$ .
- Structure: Composed of $4$ octets.
- Format: Uses Decimal numbers.
- Octet Value Range: Each octet can be $0\text{--}255$ .
- Example: 192.168.1.10
IPv6 (Internet Protocol Version 6):
- Address Length: Uses $128\text{-bit}$ .
- Structure: Composed of $8$ groups.
- Format: Uses Hexadecimal numbers.
- Example: 2001:db8::10
- Address Space: Has a much larger address space than IPv4.
IPv4 Classes:
- Class A:
  - Range: $1\text{--}127$
  - Default Mask: /8
  - Use: Very Large networks
- Class B:
  - Range: $128\text{--}191$
  - Default Mask: /16
  - Use: Medium / Large networks
- Class C:
  - Range: $192\text{--}223$
  - Default Mask: /24
  - Use: Small networks
- Class D:
  - Range: $224\text{--}239$
  - Default Mask: -
  - Use: Multicast
- Class E:
  - Range: $240\text{--}255$
  - Default Mask: -
  - Use: Experimental / Reserved

Hierarchical LAN (Local Area Network) Design:
- Structure: A hierarchical network has $3$ layers:
  - Core: Backbone
  - Distribution: Connect
  - Access: Users
Redundancy:
- Meaning: Having a backup.
Failure Domain:
- Definition: The part of the network affected when something fails.
- Rule: Smaller failure domain = Less damage.
Link Aggregation:
- Definition: Combining multiple physical links into one logical link.
- Concept: Many cables → One logical connection.
Port Density:
- Definition: How many ports a switch has.
- Fixed Configuration Switch Capacity: Typically can support up to $48$ ports.
PoE (Power over Ethernet):
- Function: Carry power to a device.
- Formula: PoE = Network cable + Power.
Multilayer Switch:
- Function: Switching + Routing.
Router:
- Function: Connects different networks.
OSPF (Open Shortest Path First):
- Type: Link-state routing protocol.
- Formula: OSPF = Routing + Large Networks + Fast Convergence.
In-Band vs Out-of-Band Management:
- In-Band:
  - Access Method: Through the network.
  - Formula: In = Internet / network.
- Out-of-Band:
  - Access Method: Used when the network connection isn't available.
  - Formula: Out = Outside the network.