Networking Fundamentals: OSI Model, Topologies, and Ethernet
1. What is a Network?
A network is a collection of interconnected computers sharing data and resources, regardless of their physical location.
2. What is the OSI Model?
The OSI (Open Systems Interconnection) Reference Model is a standardized communication model used in computer networks, defining protocols for each layer.
3. Information Transfer in the OSI Model
Information is transferred through 7 layers. Each layer covers different activities, equipment, or network protocols, defining how each level communicates with the levels above and below.
4. The First Three Layers of the OSI Model
Physical Layer: Sends bits over a physical medium, ensuring error-free transmission and reception. It defines electrical and mechanical specifications for connectors and signal timings.
Network Layer: Controls subnet operation, deciding how packets reach their destination using source and destination addresses in a predefined protocol format. It also resolves bottlenecks.
Link Layer: Groups bits from the physical layer into frames, performing error checks and acknowledgments. It detects lost or damaged frames in the physical environment.
5. Network Topologies: Advantages and Disadvantages
Bus Topology: Simple and economical, but a cable failure stops the entire network.
Star Topology: Easy troubleshooting and high fault tolerance, but more expensive due to dedicated cables for each workstation.
Tree Topology: A distributed star topology with advantages and disadvantages of both bus and star topologies.
Ring Topology: Nodes form a closed circle with unidirectional data flow. Faster, but a cable cut affects all stations. Double ring and star-ring combinations improve reliability.
6. Network Division by Geographic Area
Local Area Networks (LANs): Privately owned networks within a few kilometers, like an office or school.
Wide Area Networks (WANs): Networks extending over a large geographic area, containing multiple hosts.
7. Network Distribution by Logic
Server: Provides information or services to other network stations.
Client: Accesses information or services from servers.
Client/Server Networks: Defined roles with servers and clients.
Peer Networks: All computers can act as clients or servers.
8. Master/Slave and Intelligent Slave Concepts
Master/Slave: A master server answers queries authoritatively, while a slave server reads data from the master.
Intelligent Slave: A slave server with master server capabilities.
9. IP Protocol in the OSI Model
The IP protocol is located at layer 3, the network layer.
10. MAC Address
A unique address for each network card, consisting of 6 blocks of 2 characters.
11. IP Address
A unique 32-bit address for each computer and routing device (host).
12. Identifying Network Class
The class of an IP address is determined by the position of the first 0 in the first four bits.
13. Purpose of the Netmask
The netmask differentiates packets addressed to hosts in interconnected networks, enabling internal packet routing.
14. Network, Subnet, and Host in 175.10.20.6/24
Network Address: 175.10.0.0
Subnet Address: 175.10.20.0
Host Address: 175.10.20.6
15. TCP Layer
TCP works at layer 4, the transport layer.
16. Meaning of 84.0.0.0
Network address, Class A.
17. HUB in the OSI Model
HUB works at layer 1, the physical layer.
18. How a HUB Works
A HUB repeats the signal entering each port to all other ports, broadcasting data as required by Ethernet. It also monitors link status.
19. Bridge in the OSI Model
A Bridge works at layer 2, the data link layer.
20. How a Bridge Works
A Bridge learns MAC addresses and forwards signals based on destination. It generates a table of MAC addresses. If the destination is on the same segment, the signal is contained. If it’s on another segment, the bridge connects and repeats the signal.
23. Switch in the OSI Model
A Switch works at layer 2, the data link layer.
24. How a Switch Works
Switches analyze Ethernet frames and send them to the correct port based on the destination MAC address. They learn MAC addresses automatically, allowing multiple simultaneous transmissions without collisions.
25. Router in the OSI Model
A Router works at layer 3, the network layer.
26. How a Router Works
Routers examine IP addresses and determine the best path for packets to reach their destination, using routing tables and network topology.
27. What is Ethernet?
Ethernet is a LAN technology for transmitting data at speeds of 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet), or 1000 Mbps (Gigabit Ethernet).
28. Ethernet Media, Topologies, and Speeds
10Base2 and 10Base5: 10 Mbps, physical and logical bus topology.
10BaseT: 10 Mbps, physical star and logical bus topology.
100BaseT: 100 Mbps, physical star and logical bus topology.
100BaseF: 100 Mbps.
1000BaseT and 1000BaseF: 1000 Mbps.
Topologies: Linear, star, tree, segmented.
29. Media Access in Ethernet
Baseband: Signal transmitted without modulation, commonly used in Ethernet.
Broadband: Signal modulated like cable television, less common.
30. Ethernet Advantages and Disadvantages
Advantages: Network resilience, simple connections, cost-effective, easy device addition, centralized management.
Disadvantages: Fragile cabling, difficult troubleshooting, performance degradation with more devices, hub failure affects the entire network.
31. Meaning of 10BaseT
10 = Speed (10 Mbps)
Base = Baseband modulation
T = Twisted pair cable
32. Connecting Devices
Crossover Cable: Router-Router, Router-Switch, Hub-Hub, Router-Hub, Switch-Switch, Hub-PC, PC-PC, Switch-PC, Router-PC, Hub-Switch.
33. What is a VLAN?
VLAN: Virtual Local Area Network.
34. VLAN Configuration
VLANs are configured on switches.
35. Purpose of a VLAN
VLANs create separate broadcast domains and control Layer 2 broadcasts.