Domain 1: Networking Concepts

Clients

Devices that users access the network with (iPhone,iPad,laptop)

Servers

Provide resources to the network

Hubs

Older network devices that connect other devices like clients and server over a local area network

Switches

“Smarter hubs” that provide more security and more efficient bandwidth utilization

Wireless Access Points (WAPs/APs)

Allow wireless devices to connect a wired network

Routers

Used to connect different networks together

Firewalls

Security barriers between internal networks and the external world

Load Balancers

Devices or software that distribute network or application traffic across multiple servers

Proxy

Acts as an intermediary between a user’s device and the Internet

Intrusion Detection Systems (IDS)

Detect unauthorized access or anomalies and alert administrators

Intrusion Prevention Systems (IPS)

Not only detect threats, but also take action to prevent intrusion

Controllers

In Software-Defined Networking (SDN) context, these are central units used to manage flow control to networking devices

Network-attached Storage (NAS) Device

Dedicated file storage system that provides data access to a heterogeneous group of clients

Storage Area Network (SAN)

High-speed network that provides access to consolidated block-level data storage

Media

In networking, it refers to the physical materials used to transmit data

Wide Area Network (WAN)

Used to connect networks over large geographical areas

Client/Server Model

Utilizes a dedicated server to provide access to network resources (files, scanners, printers, etc.)

Benefits:

• Centralized management

• Great for large networks

• Good scalability

Drawbacks:

• High cost

• Specialized OS

• Has dedicated resources

Peer-to-Peer Model

Peers or other machines (e.g., laptops, desktops) can share resources together directly

Benefits:

• Lower cost

• No specialized OS

• No dedicated resources

Drawbacks:

• Decentralized management

• Inefficient for large networks

• Poor scalability

Personal Area Network (PAN)

Smallest type of wired or wireless network which usually covers a distance about 10 feet or less

Local Area Network (LAN)

Connects components in a limited distance, generally up to about 100 meters or 300 feet

Campus Area Network (CAN)

A building-centric LAN that is spread across numerous buildings in a certain area

Metropolitan Area Network (MAN)

Connects locations that are scattered across the entire city

Wide Area Network (WAN)

Connects geographically disparate internal networks

Network Topology

Refers to the arrangement of different elements like links, nodes, clients, and servers that make up a computer network

Physical Topology

Used to show how the network devices and components are physically cabled and connected together

Logical Topology

Talks about how the traffic is actually going to flow in the network

Point-to-point Topology

Simplest form of network topology that involves a direct connection between two devices

Ring Topology

A network configuration where each device is connected to two other devices, forming a circular data path

Fiber Distributed Data Interface (FDDI)

Used to conduct data transmissions on fiber optic lines in a local area network

Bus Topology

All of the network devices are connected to a single central cable, called the bus or backbone

Star Topology

Each node in the network is connected to a centralized connection point, which is normally going to be a network switch

Hub-and-spoke Topology

A variation of the star topology where the central node (hub) is connected to multiple nodes (spokes)

Mesh Topology

Features a point-to-point connection between every single device on the network to create a robust and redundant network

Full-mesh Topology:

Every node is connected to every node in the network

Partial-mesh Topology:
Some nodes are organized in a full mesh scheme, while others are only connected to one or two devices in the network

Infrastructure Mode

The most common type of wireless network that uses a wireless access point as a centralized point

Ad Hoc Mode

Decentralized wireless network which creates Peer-to-Peer connections

Wireless Mesh Topology

An interconnection of different types of nodes, devices, and radios

Datacenter

Any facility that businesses and other organizations use to organize, process, store, and disseminate large amounts of data

Collapsed Core

Network architecture where the core and the distribution layers are being merged into a single layer

Spine and Leaf Architacture

An alternative type of network architecture that focuses on the communication within the datacenter itself

North-South Flow

Traffic that enters or leaves the data center from a system physically residing outside the datacenter

East-West Flow

Refers to data flow within a datacenter

ISO Model

A conceptual framework that standardizes how different computer systems communicate over a network

Reference Model

Used to categorize the functions of a network in the OSI Model during troubleshooting efforts

7 Layers of OSI Model

Physical, Data Link, Network, Transport, Session, Presentation, Application

“Please Do Not Throw Sausage Pizza Away”

Data flow through the OSI model

Data → Data → Data → Segments → Packets → Frames → Bits

“Do Some People Fear Birthdays”

Physical Layer

Where transmission of bits across the network occurs, and includes physical and electrical network characteristics

Transition Modulation

If it changes during the clock cycle, then a 1 is represented (otherwise, a 0 is represented)

Asynchronous (Layer 1)

Uses start and stop bits to indicate when transmissions occur from the sender to the receiver

Synchronous (Layer 1)

Uses a reference clock to coordinate the transmissions by both sender and receiver

Broadband

Divides bandwidth into separate channels

Baseband

Uses all available frequencies on a medium (cable) to transmit data

Time-Division Multiplexing (TDM)

Each session takes a turn, using time slots, to share the medium between all users

Statistical Time-Division Multiplexing (StatTDM)

Dynamically allocates the time slots on an as-needed basis

Frequency-Division Multiplexing (FDM)

Divides the medium into channels based on frequencies and each session is transmitted over a different channel

Data Link Layer (2)

Packages data into frames and transmits those frames on the network

Media Access Control (MAC)

Physical addressing system of a device which operates on a logical topology

Logical Link Control (LLC)

Provides connection services and allows acknowledgement of receipt of messages

Isochronous (Layer 2)

Network devices use a common reference clock source and create time slows for transmission

Synchronous (Layer 2)

Network devices agree on clocking method to indicate beginning and end of frames and can use control characters

Asynchronous (Layer 2)

Network devices reference internal clocks and use start and stop bits for synchronization

Packet Switching

Data is divided into packets and then forwarded

Circuit Switching

A dedicated and constant communication path is maintained for the duration of a conversation

Message Switching

Data is divided into messages which may be stored and then forwarded

Route Discovery and Selection

Manually configured as a static route or dynamically through a routing protocol

Connection Services

Augment Layer 2 connection services to improve reliability

Internet Control Message Protocol (ICMP)

Sends error messages and operational information to an IP destination

Transport Layer (4)

Dividing line between the upper layers and the lower layers of the OSI model

Transmission Control Protocol (TCP) (Layer 4)

Sits at the transport layer and provides reliable, ordered, and error-checked delivery of data between application over a networkapplications

User Datagram Protocol (UDP) (4)

Connectionless protocol that is an unreliable way to transport segments across the network

TCP versus UDP (4)

TCP:

Reliable, Connection-oriented, Segment retransmission and flow control through windowing, Segment sequencing, Acknowledges segments

UDP:
Unreliable, Connectionless, no windowing or retransmission, no sequencing, no acknowledgment

Windowing (4)

Occurs by allowing the receiver to specify the amount of data it can handle at a time

Buffering (Layer 4)

Occurs when devices allocate memory to store segments if bandwidth is not readily available

Session Layer (5)

Keeps conversations separate to prevent intermingling of data

Set Up Session (Layer 5)

Checking of user credentials and assigning numbers to sessions to help identify them

Maintain Session

Where data transfer back and forth over the network

Tear Down Session

Ending of a session after the transfer is done or when the other party disconnects

H.323 (5)

Used to set up, maintain, and tear down voice and video connections

NetBIOS

Used to share files over a network

Presentation Layer (6)

Formats the data to be exchanged and secures that data with proper encryption

Data Formatting (6)

Data is formatted by the computer to have compatibility between different devices

Encryption

Used to scramble the data in transit to keep it secure from prying eyes and provide data confidentiality

Application Layer (7)

Provides application-level services where users communicate with the computer

Application Services

Unites communicating components from more than one network application

Service Advertisement

Sending out of announcements to other devices on the network to state the services they offer

Protocol Data Unit (PDU)

A single unit of information transmitted in a computer network

SYN (Synchronization)

Used to synchronize connection during the three-way handshake

ACK (Acknowledgement)

Used during the three-way handshake, but also used to acknowledge the successful receipt of packets

FIN (Finished)

Used to tear down the virtual connections created using the three-way handshake and the SYN flag

RST (Reset)

Used when a client or server receives a packet that it was not expecting during the current connection

PSH (Push)

Used to ensure data is given priority and is processed at the sending or receiving ends

URG (Urgent)

Similar to PSH and identifies incoming data as urgent

MAC Address

Physical address that is used to identify a network card on a local area network

EtherType

Used to indicate which protocol is encapsulated in the payload of a frame

Port

Virtual entry/exit point for communications used by software applications to exchange information

Protocol

Set of rules and conventions for data exchange between network devices

Ephemeral Ports

Short-lived temporary ports which are opened for just a small period of time from a predefined range of ports

Internet Control Message Protocol (ICMP)

Integral part of the Internet Protocol Suite which is a set of networking protocols used on the Internet

ICMP Flood Attack

Type of attack that involves overwhelming a target machine with a large number of ICMP Echo Request packets

Distributed Denial of Service (DDoS) Attack

Where the attacker usually uses a network of compromised computers (called botnet) to generate significant amount of traffic

Ping of Death

Attack that exploits a vulnerability that existed in older, unpatched systems where the attacker sends malformed or oversized packets using the ICMP protocol