Network Fundamentals

Network Fundamentals

• Networks connections extend through both wireless and wired mediums.

Network Components

• Clients include devices that users utilize to access networks, such as workstations, laptops, and tablets.
• Servers provide network resources like email and shared files.
• Hubs connect devices using older tech that is not commonly used due to limitations.
• Switches are smarter hubs that ensure secure and efficient bandwidth utilization.
• Wireless Access Points (WAPs) enable wireless devices to connect to a wired one using radio frequency waves.
• Routers connect different networks and make intelligent forwarding decisions based on IP addresses.
• Firewalls serve as security barriers between internal networks and the internet to monitor and control traffic.
• Load Balancers distribute network/application traffic across servers, preventing bottlenecks.
• Proxy Servers act as intermediaries enhancing security and privacy.
• Intrusion Detection Systems (IDS) are used for detecting unauthorized access or anomalies.
• Intrusion Prevention Systems (IPS) detect and act to prevent intrusions.
• Controllers help manage flow control in software-defined networking (SDN), offering flexibility and efficiency.
• Network-attached Storage (NAS) devices are dedicated file storage systems providing data access to authorized clients.
• Storage Area Networks (SANs) are high-speed networks for consolidated block-level data storage, enhancing accessibility.
• Media includes physical data transmission materials like copper and fiber optic cables.
• Wide Area Network (WAN) links connect networks over large areas and are essential for global connectivity.

Network Components Takeaway

• Understanding network components is crucial for efficient, secure data transmission, aiding in network design, management, problem-solving, and security implementation.

Network Resources

• The Client/Server Model utilizes a dedicated server for centralized access to files, printers, and scanners
• The Client/Server Model allows easy administration and backup due to a central server

Client/Server Model Benefits

• Centralized administration.
• Easier management.
• Better scalability.

Client/Server Model Drawbacks

• Higher infrastructure cost.
• Requires dedicated hardware and specialized skillset.

Client/Server Model

• A leading model in business networks.

Peer-to-Peer Model

• Direct sharing of resources among peers, such as laptops and desktops.
• The peer-to-peer model makes administration and backup difficult due to dispersed files on different machines.
• Drawbacks include redundancy, complex management, and scalability issues.
• The Peer-to-Peer model is useful for low-cost setups.

Peer-to-Peer Model Benefits

• Low cost.
• Does not require specialized infrastructure or hardware.

Peer-to-Peer Model Drawbacks

• Decentralized management.
• Poor scalability for large networks.
• Not recommended for business networks.

Network Geography

• Personal Area Network (PAN): It is the smallest network type, it covers about 10 feet or less, includes Bluetooth and USB connections within arm's reach.
• Local Area Network (LAN): It is common in office buildings, limited to 100 meters, use CAT 5 cabling, WiFi (IEEE 802.11) or Ethernet (IEEE 802.3)
• Common LANs include offices, schools, and homes.
• Campus Area Network (CAN): It is building-centric, spans numerous buildings in an area, covers several miles, e.g., college campuses/business parks.
• Metropolitan Area Network (MAN): It connects locations across the entire city, larger than CAN, covers up to 25 miles, includes city departments and multiple campuses
• Wide Area Network (WAN): It geographically disparate internal networks, offers large geographic coverage across states/countries and consists of lease lines/VPNs

Important Network Standards

• PAN uses Bluetooth and USB
• LAN uses IEEE 802.3 (Ethernet)
• CAN connects multiple LANs
• MAN spans an entire city
• WAN connects internal networks globally

Network Geography Memory Aid

• PAN (Personal Area Network) reaches an arm's length.
• LAN (Local Area Network) stretches <100 meters.
• CAN (Campus Area Network) spans buildings.
• MAN (Metropolitan Area Network) stretches across the city, up to 25 miles
• WAN (Wide Area Network) is geographically extensive, even global

Wired Network Topology

• Network Topology refers to the arrangement of elements in a computer network, including links, nodes, clients, and servers.

Diagram Types

• Physical Topology describes physical cabling and device connections
• Physical Topology represents the real-world layout using floorplans.
• Logical Topology describes how data flows in the network.
• Logical Topology focuses on the logical connection rather than physical placement.

Six Wired Network Topologies

• Point-to-Point Topology: A direct connection between two devices, simple, reliable for small-scale connections, not scalable.
• Ring Topology: Each device connects to two others in a circular data path; unidirectional flow prevents collisions.
• Star Topology: Each node connected to a central point (network switch); robust, but network depends on the central point's functionality.
• Hub-and-Spoke Topology: A variation of star topology with a central hub connects to multiple spokes; less expensive for larger networks.
• Mesh Topology: Point-to-point connections between every device for redundancy; robustness is costly and complex.

Network Interconnections

• Bus Topology connects all devices to the same central cable (bus).
• Bus Topology’s data is accessible to all, but only the intended recipient processes it, easy to install.
• Bus Topology is an older technology not common in modern networks.

Mesh Topology variations and Formula

• Full mesh topology connects every node to every other
• Partial mesh topology connects some nodes fully, others connected to only 1-2 other nodes
• Formula for connections in a mesh topology is n(n-1)/2, where n is the number of nodes

Network Topology Benefits

• Understanding different topologies is crucial for network design.
• Each topology has unique advantages and disadvantages.
• Practicality varies based on the scale and requirements of the network.

Wireless Network Topology

• Infrastructure Mode has a centralized wireless network with a wireless access point, similar to a star topology, common in homes, and supports security controls.
• Ad Hoc Mode is a decentralized wireless network, operates like a peer-to-peer network, has no routers or access points, connects devices directly.
• Wireless Mesh is a unique interconnection of nodes, devices, and radios creating a mesh topology, combines various technologies.

Wireless Network Topology Technologies

• Bluetooth
• WiFi
• Microwave
• Cellular
• Satellite

Wireless Network Topology

• Enables large-scale access in harsh environments and uses different radio frequencies.

Wireless Mesh Uses

• Post-disaster scenarios.
• Humanitarian assistance missions.
• Combining microwave, satellite, cellular, and WiFi for reliable and redundant networks.
• Satellite for long distances.
• Microwaves for medium ranges.
• Wireless for short distances.

Datacenter Topology

• Datacenter is any facility where networked computers organize and share large amounts of data.

Three-Tiered Hierarchy uses

• Core Layer Houses high-performance routers, merging geographically separated networks; backbone of the network.
• Distribution/Aggregation Layer provides boundary definition using access lists/filters and defines policies.
• Access/Edge Layer connects endpoint devices using regular switches and delivers packets to the correct end devices.

Benefits of the Three-Tiered Hierarchy topology

• Better Performance.
• Improved Management.
• Scalability.
• Redundancy.
• This topology allows troubleshooting by isolating each layer for maintenance and problem detection.

Data Center Alternative Topologies

• Collapsed Core is a network architecture where the core and distribution layers are merged.
• Spine and Leaf Architecture focuses on communication within datacenters and particularly server farms.

Main Spine and Leaf Architecture Characteristics

• Consists of a set of leaf switches that connect to servers
• Consists of a set of spine switches that interconnect all leaf switches in a full-mesh topology

Spine and Leaf Architecture

• Enhances speed.
• Works well with a Software Defined Network (SDN)

Traffic Flow Topologies

• North-South Traffic enters (Southbound traffic) or leaves (North traffic) the data center.
• East-West Traffic refers to data flow within a datacenter.

OSI Model

• The Open Systems Interconnect Model(OSI) was developed in 1977 by the International Organization for Standardization; it uses a reference model to categorize network functions for troubleshooting.
• Networks today operate under the TCP/IP mode

OSI Model Layers

• Layer 1: Physical
• Layer 2: Data Link
• Layer 3: Network
• Layer 4: Transport
• Layer 5: Session
• Layer 6: Presentation
• Layer 7: Application

Data and the OSI Model

• Data undergoes changes as it flows through the OSI,
• Bits - Layer 1
• Frames - Layer 2
• Packets - Layer 3
• Segments - Layer 4
• Data - Layers 5, 6, 7

Layer 1

• Physical Layer Overview: Data transmission as bits include physical & electrical network characteristics.
• Data type occurs as bits which are binary (1s and 0s)
• Modulation is used by switching between levels to represent 1 or 0
• Copper Wire (Cat5/Cat6) uses voltage (0V for 0, +5V/-5V for 1)
• Fiber Optic Cable uses light (on for 1, off for 0)

Layer 1 Connectors and Standards

• RJ-45 Connector is used in CAT5/CAT6 cables.
• Wiring standards include TIA/EIA-568A, TIA/EIA-568B
• Crossover cables mix TIA/EIA standards at each end; straight-through cables use the same TIA/EIA at both ends.

Physical Topology and connections

• Different network layouts include bus/ring/star/mesh setups
• Connections are based on how cables are physically connected.
• Asynchronous Communication uses start/stop bits for out-of-sync data transmission.
• Synchronous Communication uses real-time transmission with a common time source.
• Broadband divides bandwidth into channels, with different users using different frequencies.
• Baseband uses all frequencies of the cable all the time.

Layer 1 Multiplexing

• Multiplexing takes limited resources and then efficiently enables multiple people to use a baseband connection at the same time.
• Time Division Multiplexing (TDM) allocates dedicated time slots.
• Statistical Time Division Multiplexing (StatTDM) allocates time slots based on when capacity is needed dynamically.
• Frequency Division Multiplexing (FDM) divides the medium into channels.

Layer 1 Devices

• Media cables include fiber optic, Ethernet, and coaxial cable.
• Wireless media includes Bluetooth, Wi-Fi, and near-field communication.
• Infrastructure devices include hubs, access points, and media converters.

Layer 1 Device Characteristics

• Repeats all incoming signals.
• Has no logic or decision-making capabilities.

Layer 2

• Data Link Layer is responsible for packaging bits from Layer 1 into frames for network transmission and provides error correction, flow control, and MAC addressing.
• MAC Address: A 48-bit system identifies devices to operate on a logical topology with a unique address for every NIC.
• MAC Addresses are written in hexadecimal numbers.
• The first 24 bits identify the manufacturer and the last 24 bits the specific device.
• Media Access Control (MAC) address is crucial for the logical topology.
• Logical Link Control (LLC) provides connection services and acknowledges message receipt.

LLC details

• Most basic form of flow control for preventing receiver overwhelm.
• LLC utilizes checksums for corrupted data frames.

Layer 2 Synchronization Methods

• Isochronous Mode: Methods use a common reference clock, allocating time slots with less overhead.
• Synchronous Mode: Uses the same clock with beginning/end frame control characters.
• Asynchronous: Devices reference own clock cycles without strict control of communication timing.

Layer 2 Devices

• Network Interface Cards (NICs).
• Bridges.
• Switches use logic to learn and send data to specific devices based on MAC addresses.
• CAM tables identify physical ports for selective transmission.

Layer 3

• The network layer concerns routing and forwarding traffic, using logical addresses, such as IP.
• IPv4 is written in dotted octet notation as these are four sets of numbers separated by four dots, such as 172.16.254.1.
• Packet Switching/Routing divides data into packets, then forwards them.
• Circuit Switching sets up a dedicated link.
• Message Switching stores messages and then forwards them.

Layer 3 Network Routing Method

• Routers utilize routing tables that determine the best path, using dynamic protocols, such as RIP and also OSPF.
• Augments Layer 2 services with flow control and ensures packat is reordering.

ICMP

• ICMP messages send error and operational information.

ICMP testing tools

• PING that tests connectivity.
• Traceroute traces data transmission route.

Layer 3 Devices and Protocols

• Routers.
• Multi-layer switches that combine Layer 2/Layer 3 features - a switch is always a Layer 2 device
• If mentioned as a multi-layer switch, it implies they are operating as a Layer 3 device
• IPv4.
• IPv6.
• ICMP.

Layer 4

• The transport Layer’s line divides the upper layers and lower layers of the OSI model.

Layer 4 Upper Layers include

• Transport.
• Session.
• Presentation.
• Application.
• Segments are the data type in the Transport Layer. TCP, the Transmission Control Protocol, is connection-oriented for ensuring reliable network segment transmission using acknowledgements. Three-Way Handshake is used by TCP

TCP Three-Way Handshake

• SYN - synchronization.
• SYN-ACK – synchronization - acknowledgement.
• ACK - acknowledgement.
• TCP (Transmission Control Protocol) uses windowing.
• Connectionless protocol UDP gives unreliable transport of segments (datagram) with NO handshake, less overhead, or acknowledgement and retransmission.

Exam Note

• Segment is TCP data type; Datagram is a UDP data type.

Comparing TCP and UDP

• TCP is reliable with a three-way handshake, connection-oriented, segment retransmission, flow control, sequencing, segment acknowledgment.
• UDP is unreliable without three-way handshake and has connectionless characteristics; it does not support retransmission, sequencing, or acknowledgment.

Layer 4 Windowing

• Clients can adjust the amount of data in each segment and optimize throughput.
• Opens or closes windows based on retransmissions.
• Occurs when devices allocate memory to segments to prevent overflow.

Layer 4 Devices

• TCP and UDP protocols.
• WAN accelerators.
• Load balancers and firewalls.

Layer 5 (Session Layer) functions

• Manages sessions to prevent data intermingling through user credentials.
• Continuous data transfer between parties.
• Includes acknowledgement of data transfers.
• Tearing down sessions occurs when communication goals are achieved or one party disconnects.

Layer 5 protocols

• H.323 sets up, maintains, and tears down voice/video connections; it operates over RTP.
• NetBIOS allows file sharing over a network and is associated with Windows.

Exam note

• Layer 5 issues relate to protocols and software rather than specific devices
• It formats, encrypts, and secures data exchange between devices.

Layer 5 protocols

• Transport Layer Security (TLS) ensures secure data transfer; creates an encrypted tunnel.
• Standard languages control how ASCII text is displayed.

Important Languages

• HTML
• XML
• PHP
• JavaScript

Standard text formats

• Display text using ones and zeros.
• Different image (GIF/JPEG/TIFF) formats and file formats, such as MP4, MPEGs, and MOV

Encryption Algorithms and Security

• Scrambles data to ensure confidentiality and security during transit and storage.
• TLS
• SSL (Secure Sockets Layer)

Layer 7

• Application Layer is the user-computer interface, providing application-level services with file and network transfers.
• Applications unite components for more than a single network application like file/email sharing with varied low-level protocols (POP3, IMAP, SMTP) and also involves client-server processes.

Important Advertisement protocols

• Printers and file servers managed by Active Directory.
• Self-advertising devices like wireless printers.

Layer 7 Protocols

• Email Applications via POP3, IMAP, SMTP, are very commonly encountered
• DNS
• HTTP

Network Process

• Encapsulation adds headers/trailers around data.
• Decapsulation removes applied encapsulates to read data.
• Moving down from Layer 7 to Layer 1 involves encapsulation.
• Moving from Layer 1 to 7 involves decapsulation.

Protocol Data Units

• OSI Model: PDU is a single unit of information transmitted in a computer network.
• Layers are written with L (layer number) PDU, e.g., L7 PDU.
• Special names are used for the PDU of layers 1,2,3 and 4

Named PDUs

• Layer 1 – Bits
• Layer 2 – Frames
• Layer 3 – Packets
• Layer 4 – Segments (TCP) or Datagrams (UDP)
• TCP Header is Layer 4 with 10 fields and 20 bytes of information, including source/destination ports and acknowledgment numbers.

TCP control flags details

• SYN - synchronizes the connection in a three-way handshake.
• ACK - acknowledges the successful receipt of data.
• FIN (Finished) – tears down the handshake.
• RST (Reset) is used upon receiving an unexpected packet.
• PSH (Push) ensures priority.
• URG (Urgent) identifies incoming data as urgent.
• UDP Header is Layer 4, uses an 8-byte header with Length indicating total packet bytes and also non-mandatory checksum testing
• IP Headers, Layer 3 contains various fields with Version, Type of Service, and Fragmented offset

Ethernet Header details

• Layer 2 features destination/source media access control which is used to identify a network card Processed by switches.
• EtherType field indicates protocol encapsulated in payload frame, such as IPv4 or IPv6
• VLAN Tag is an optional field using an IEEE 802.1Q or IEEE 802.1AD standard.
• Frames are sent at Layer 2 and contain a Payload for transferring data, either 42 bytes when using VLAN or 46 bytes when no VLANs are involved
• Maximum Transmission Unit (MTU) has a payload sizes of 1500 bytes

Frames vs Packages

• Jumbo Frames exceed the standard 1500 bytes and need reconfiguration
• Encapsulation occurs when each layer adds a header and, while decapsulation removes each of the intermediate devices and encapsulates at Layer 7.