Network Basics Overview

Overview of Network Basics

• Network is a system of interconnected devices that can communicate and exchange data
• The OSI (Open System Interconnection) model describes how networks function in 7 layers
• The 7 layers are: Application, Presentation, Session, Transport, Network, Data Link, and Physical
• Each layer has a specific role and set of protocols that enable end-to-end data communication

Application Layer

• Responsible for user interaction and applications
• Examples include email servers, web browsers, FTP, DNS
• Provides protocols like HTTP, SMTP, DHCP for application-level functionality

Presentation Layer

• Responsible for data representation and formatting
• Converts data to/from formats understandable by applications
• Handles things like text encoding, encryption, compression

Session Layer

• Establishes, maintains and synchronizes communication sessions
• Provides mechanisms for checkpointing, recovering, restarting sessions
• Manages login sessions, timeouts, and session state

Transport Layer

• Ensures reliable and in-order delivery of data packets
• Provides protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol)
• TCP offers reliable delivery with error-checking, while UDP is faster but less reliable

Network Layer

• Responsible for logical addressing and routing of data
• Handles IP (Internet Protocol) addressing and path determination
• Ensures data reaches the correct destination

Data Link Layer

• Handles physical addressing and local network access
• Provides error-checking and flow control at the link level
• Defines how data is formatted, encoded, and processed on the physical medium

Physical Layer

• Concerned with the physical equipment involved in the network

• Defines electrical, mechanical, functional and procedural standards

• Includes cables, connectors, signal transmission, etc.### Internet Infrastructure and Protocols

• The Internet consists of various network devices and interconnections that enable communication and data transfer

• Key devices in the network include:

  • Routers: Responsible for forwarding data packets between networks
  • Switches: Connect multiple devices within a local network
  • Computers/Devices: End-user devices that generate and receive data

• Data transmission on the Internet follows standardized protocols:

  • TCP/IP (Transmission Control Protocol/Internet Protocol): Fundamental protocols that enable end-to-end data transfer
  • OSI (Open Systems Interconnection) Model: Conceptual framework describing 7 network layers, from physical to application

IP Addressing

• IP (Internet Protocol) addresses uniquely identify devices on the network
• IP addresses are divided into classes, each with a defined range:
  • Class A: 1.0.0.0 to 127.255.255.255
  • Class B: 128.0.0.0 to 191.255.255.255
  • Class C: 192.0.0.0 to 223.255.255.255
• Devices are assigned IP addresses within these class ranges
• Subnet masks further divide the IP address space to create logical subnetworks

Network Device Configuration

• Routers and switches require configuration to connect and route data
• Key configuration steps:
  • Enable the router/switch interface
  • Assign an IP address and subnet mask
  • Configure the default gateway (router's IP address)
  • Optionally, set other parameters like DNS servers

Troubleshooting Connectivity

• Use tools like Ping to test connectivity between devices
  • Ping sends ICMP echo requests and measures response times
  • Successful ping indicates the target device is reachable
• Trace route (tracert) can be used to identify the path and latency between two points
• Network diagnostics can isolate connectivity issues at the device, network, or application level

Internet Governance

• ICANN (Internet Corporation for Assigned Names and Numbers) coordinates the global Internet's unique identifier systems

  • Manages the Domain Name System (DNS) and IP address allocation
  • Operates as a non-profit multi-stakeholder organization

• Regional Internet Registries (RIRs) are responsible for IP address distribution within their respective regions

  • Examples: ARIN (North America), RIPE NCC (Europe), APNIC (Asia-Pacific)### Network Protocols and Routing Configuration

• The OSPF (Open Shortest Path First) protocol is a routing protocol used to determine the best path for network traffic

• OSPF uses a hierarchical network design with areas, where each area has a designated router called the Designated Router (DR)

• The DR is responsible for maintaining the OSPF link-state database and communicating changes to other routers

• Routers in an OSPF network use multicast to communicate with each other, sending "hello" packets to discover and maintain neighbor relationships

• If a router's link fails, it will send an update to the DR, which will then propagate the update to the other routers

• This allows the network to converge quickly and adapt to changes, ensuring reliable connectivity

Designated Router (DR) and Backup DR (BDR)

• In OSPF, one router in each area is elected as the Designated Router (DR)
• The DR is responsible for creating and maintaining the link-state database for the area
• A Backup Designated Router (BDR) is also elected to take over if the DR fails
• The DR and BDR form a special relationship, with the DR handling all link-state updates and the BDR listening in case it needs to take over
• This hierarchical structure helps improve network scalability and efficiency

Router Prioritization and Election

• Routers in an OSPF network can be configured with a priority value to influence the DR/BDR election process
• Routers with a higher priority are more likely to be elected as the DR or BDR
• The router with the highest priority in the area will be elected as the DR, and the router with the second-highest priority will be elected as the BDR
• If priorities are equal, the router with the highest router ID (typically the highest IP address) will be elected

Routing Information Dissemination

• OSPF uses multicast addresses to communicate routing information between routers
• The designated multicast address for OSPF is 224.0.0.5, which is used for regular OSPF updates
• There is also a designated multicast address of 224.0.0.6 that is used specifically for communication between the DR and BDR
• This allows routing updates to be efficiently distributed to all routers in the network, reducing overhead and improving scalability

Network Resilience and Failover

• If a router's link fails, it will send an update to the DR, which will then propagate the update to the other routers
• This allows the network to quickly converge and adapt to changes, ensuring reliable connectivity
• If the DR fails, the BDR will take over its responsibilities, ensuring continuity of network operations
• Routers can also be configured with different priority levels, allowing the network to automatically elect a new DR/BDR in the event of a failure

Key Takeaways

• OSPF is a hierarchical routing protocol that uses a Designated Router (DR) and Backup DR (BDR) to manage the network
• Routers communicate using multicast to efficiently distribute routing updates
• The network can quickly adapt to changes and failures, ensuring reliable connectivity
• Proper configuration of router priorities is important to ensure the right routers are elected as DR and BDR

Network Basics

• A network is a system of interconnected devices that can communicate and exchange data.
• The OSI model describes network function in 7 layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.
• Each layer has a specific role and set of protocols for end-to-end data communication.

OSI Layers

Application Layer

• Responsible for user interaction and applications, including email servers, web browsers, FTP, and DNS.
• Provides protocols like HTTP, SMTP, and DHCP for application-level functionality.

Presentation Layer

• Responsible for data representation and formatting.
• Converts data to/from formats understandable by applications.
• Handles text encoding, encryption, and compression.

Session Layer

• Establishes, maintains, and synchronizes communication sessions.
• Provides mechanisms for checkpointing, recovering, and restarting sessions.
• Manages login sessions, timeouts, and session state.

Transport Layer

• Ensures reliable and in-order delivery of data packets.
• Provides protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).
• TCP offers reliable delivery with error-checking, while UDP is faster but less reliable.

Network Layer

• Responsible for logical addressing and routing of data.
• Handles IP addressing and path determination.
• Ensures data reaches the correct destination.

Data Link Layer

• Handles physical addressing and local network access.
• Provides error-checking and flow control at the link level.
• Defines how data is formatted, encoded, and processed on the physical medium.

Physical Layer

• Concerned with the physical equipment involved in the network.
• Defines electrical, mechanical, functional, and procedural standards.
• Includes cables, connectors, signal transmission, etc.

Internet Infrastructure and Protocols

• The Internet consists of various network devices and interconnections that enable communication and data transfer.
• Key devices in the network include routers, switches, and computers/devices.
• TCP/IP (Transmission Control Protocol/Internet Protocol) and OSI Model are fundamental protocols and frameworks for the Internet.

IP Addressing

• IP addresses uniquely identify devices on the network.
• IP addresses are divided into classes: Class A (1.0.0.0 to 127.255.255.255), Class B (128.0.0.0 to 191.255.255.255), and Class C (192.0.0.0 to 223.255.255.255).
• Devices are assigned IP addresses within these class ranges.
• Subnet masks further divide the IP address space to create logical subnetworks.

Network Device Configuration

• Routers and switches require configuration to connect and route data.
• Key configuration steps include:
  • Enabling the router/switch interface.
  • Assigning an IP address and subnet mask.
  • Configuring the default gateway (router's IP address).
  • Optionally setting other parameters like DNS servers.

Troubleshooting Connectivity

• Use tools like Ping to test connectivity between devices.
• Ping sends ICMP echo requests and measures response times.
• Successful ping indicates the target device is reachable.
• Trace route (tracert) can be used to identify the path and latency between two points.
• Network diagnostics can isolate connectivity issues at the device, network, or application level.

Internet Governance

• ICANN (Internet Corporation for Assigned Names and Numbers) coordinates the global Internet's unique identifier systems.
• Manages the Domain Name System (DNS) and IP address allocation.