Final Notes on Network Layer Characteristics (PDF)

Final Notes module 8 24F-ITNModule_8 Updated Network Layer Characteristics Introduction to the Network Layer Purpose: Enables end devices to exchange data Protocols: IPv4 and IPv6 are primary communication protocols Basic Operations: Addressing end devices Enc...

Final Notes module 8 24F-ITNModule_8 Updated Network Layer Characteristics Introduction to the Network Layer Purpose: Enables end devices to exchange data Protocols: IPv4 and IPv6 are primary communication protocols Basic Operations: Addressing end devices Encapsulation, Routing, De-encapsulation IP Encapsulation IP encapsulates the transport layer segment Addressing remains unchanged throughout its journey Connectionless Nature of IP No connection established prior to sending packets IP does not require control information Best Effort Delivery No guarantee of packet delivery Reduced overhead, no resending of lost packets Media Independence IP operates independently of media types (copper, fiber, wireless) Works without concern for data link layer frames Maximum Transmission Unit (MTU) Established by the network layer based on data link layer control information  Fragmentation occurs when IPv4 packets are split for transmission IPv4 Packet Header Characteristics of the IPv4 Header Purpose: Directs packets to correct destinations and processes for routing Fields Include: Source/Destination IPv4 addresses, Version, TTL (Time to Live) Significant Header Fields Version: 4 for IPv4 Total Length: Size of packet including header Protocol: Identifies next level protocol (TCP, UDP, etc.) IPv6 Overview Limitations of IPv4 Address depletion: Running out of IPv4 addresses End-to-end connectivity issues: Due to NAT complexities Increased network complexity: Side effects of NAT usage Benefits of IPv6 Large address space (128 bits) Improved packet handling No need for NAT; facilitates direct communication IPv6 Packet Header Fields Simplified header includes fewer fields Significant fields similar to IPv4 with enhancements Host Routing Decisions Packet Routing Basics Packets created at the source device Host maintains its routing table for local, LAN, and remote destinations Default gateway is required for routing outside the local network Features of Default Gateway Must be on the same IP range as the LAN Facilitates traffic forwarding to other networks Host Routing Tables Can be viewed using route print or netstat -r Displays interfaces and both IPv4 and IPv6 routing tables Introduction to Routing Routing Table Types Directly Connected: Automatically added by active interfaces Remote: Learned through static or dynamic routing Default Route: Used when no matching route is found Static vs Dynamic Routes Static Routes: Manually configured, adjusted during topology changes Dynamic Routes: Automatically discover and maintain routing information Module 9: Address Resolution Key Topics: 1. MAC and IP Addressing: Devices on a local network use MAC addresses for Layer 2 communications. IP addresses (Layer 3) are used for routing packets between devices on different networks. 2. Address Resolution Protocol (ARP): Maps IPv4 addresses to MAC addresses. Resolves local or gateway MAC addresses for communication. Commands to view ARP tables: Cisco: show ip arp Windows: arp -a 3. ARP Vulnerabilities: ARP spoofing can cause security threats like ARP poisoning. Modern networks mitigate these with enterprise-level switches.  4. IPv6 Neighbor Discovery Protocol: Replaces ARP in IPv6. Uses ICMPv6 messages like Neighbor Solicitation (NS) and Neighbor Advertisement (NA). Module 10: Basic Router Configuration Key Topics: 1. Initial Router Settings: Set hostname, secure access (passwords for EXEC modes, encryption), and configure banners. Save configuration to NVRAM. 2. Interface Configuration: Assign IP addresses to router interfaces (IPv4 and IPv6). Activate interfaces with no shutdown. 3. Verification Commands: show ip interface brief and show ipv6 interface brief to check interface statuses. show ip route and show ipv6 route for routing tables. 4. Default Gateway: Hosts and switches need configured default gateways for remote communications. Module 11: IPv4 Addressing Key Topics: 1. IPv4 Structure: Composed of a network portion and a host portion, defined by a subnet mask. Logical ANDing is used to determine network addresses. 2. Address Types: Unicast: One-to-one communication. Broadcast: One-to-all on the same network. Multicast: One-to-many group addresses. 3. Subnetting:  Divides networks into smaller, efficient subnets. CIDR and VLSM techniques optimize IP usage. 4. Private vs. Public Addresses: NAT translates private IPs to public IPs for internet access. Module 12: IPv6 Addressing Key Topics: 1. IPv6 Basics: 128-bit address space; represented in hexadecimal. Supports larger address spaces and better security than IPv4. 2. Address Types: Unicast: Unique to a single device. Multicast: Communicates to multiple devices. Anycast: Routes to the nearest device. 3. Dynamic Addressing: Methods like SLAAC, stateless DHCPv6, and stateful DHCPv6. 4. Subnetting in IPv6: Uses a 16-bit subnet ID field between the Global Routing Prefix and Interface ID. Subnet IDs allow efficient allocation and management. Module 13: ICMP Messages and Connectivity Tests ICMP Overview: Provides error messaging and operational checks for IPv4 (ICMPv4) and IPv6 (ICMPv6). Key messages include echo (ping), destination unreachable, and time exceeded. Ping and Traceroute Tests: Ping: Tests connectivity using ICMP echo requests and replies. Traceroute: Identifies the path and routers to a destination using TTL or Hop Limit. Module 14: Transport Layer TCP and UDP: TCP: Reliable, stateful, ensures data order with features like retransmissions and flow control.  UDP: Lightweight, connectionless, suitable for latency-sensitive applications like video streaming. Port Numbers: Enables multiple conversations; categorized into well-known, registered, and dynamic ranges. TCP Communication: Establishes sessions through a three-way handshake, manages data flow, and terminates sessions with FIN flags. Module 15: Application, Presentation, and Session Layers Key Application Layer Protocols: Includes HTTP, FTP, SMTP, DNS, DHCP, and IMAP. Presentation and Session Layers: Presentation: Formats, compresses, and encrypts data. Session: Manages dialog creation and maintenance. P2P Networks and Applications: Facilitates decentralized resource sharing with applications like BitTorrent and Skype. Module 16: Network Security Fundamentals Threats and Vulnerabilities: Physical (hardware damage), environmental, and maintenance issues. Malware types include viruses, worms, and ransomware. Attacks: Reconnaissance (e.g., port scanning), access attacks (password cracking), and DoS/DDoS. Mitigation Strategies: Defense-in-Depth: Layers of security like firewalls, VPNs, and anti-virus software. Backups and Updates: Regular data and configuration backups; timely system patching. AAA: Authentication, Authorization, and Accounting. Endpoint Security: Protects individual devices via policies and tools. Module 17: Small Network Management Network Design for Small Networks: Redundancy: Reduces single points of failure with duplicate equipment and links. Traffic Management: Employs QoS to prioritize real-time traffic like voice and video. Scaling Networks: Requires documentation, inventory, budget planning, and traffic analysis. Connectivity Verification: Tools like ping and network baselines help identify and troubleshoot issues.