Internet Architecture & Network Layer - Page-by-Page Notes

Page 1

  • Internet Architecture & Network Layer
  • Internet: global information/communication system that links thousands of local networks.
  • Enables exchange of information between two or more computers on a network.
  • Supports transfer of messages via mail, chat, video Conferencing, etc.

Page 2

  • Parts of the Internet include: end systems/hosts, intermediate devices (modem/packet switch), routers, servers, hubs, etc.
  • Infrastructure involves providers, base stations, regional ISP servers, and various network devices connecting hosts.
  • Communication links can be wired or wireless (types include coaxial cables, copper wires, optical fiber, radio spectrum).
  • Packet switching connects end systems through nodes; direct end-to-end connection is not required.

Page 3

  • Internet is made up of: hosts, packet switches, regional ISP servers, base stations, nodes, mobile devices, etc.
  • Connection involves traditional and non-traditional devices acting as hosts/end systems interconnected via communication links and nodes.
  • Types of communication links include coaxial cables, copper wires, optical fiber, and radio spectrum.
  • Packet switching uses intermediate nodes to forward packets between end systems.

Page 4

  • Internet services fall into two types:
    • Communication services
    • Information retrieval services
  • Examples of communication services: E-mail, FTP, Telnet, chat, etc.
  • Information retrieval services refer to accessing information from networks/databases.

Page 5

  • Internet protocols: TCP/IP (Transmission Control Protocol & Internet Protocol).
  • Primary protocols: TCP and IP; IP handles movement of data between hosts; data is carried in packets.
  • Protocol suite is layered, with each layer handling different aspects of communication.
  • IP provides simple naming/addressing to locate resources on the Internet.
  • Information or data on Internet is carried in packets; an IP packet contains sender and recipient addresses (IP addresses).

Page 6

  • Router: forwards packets along the network; figures show router followed by packets.
  • Routers perform routing decisions to deliver packets toward their destination.

Page 7

  • Domain name / Domain: A smaller network making up the Internet with many computers; examples: in-India, gov.gov.
  • Intranets: private networks used by a company/organization.
  • Main aims of intranet: safe staff communication, information archiving, and teamwork; social intranet features; data security.
  • Intranets protect data and offer data security within an organization.

Page 8

  • Structure of Intranet: internal servers, firewall, PCs, and connected devices.
  • Advantages of Intranet:
    • Easy administration
    • Deployment speed
    • Functional capabilities
  • Disadvantages:
    • Security risks
    • High costs
    • Limited scalability
    • Technical issues/rollouts
    • Maintenance overhead
    • Data redundancy
    • Limited access
    • Lack of flexibility

Page 9

  • Difference between Internet and Intranet:
    • Internet: public network; open access; unlimited users; less secure; no single owner; wide area coverage; system failures are less predictable.
    • Intranet: private network; restricted access to organization members; limited users; secure; owned/controlled by an organization; restricted coverage; failures are more predictable due to monitoring.

Page 10

  • Network Layer vs Data Link Layer:
    • Data Link Layer: moves a frame across a single link from one end to the other.
    • Network Layer: provides end-to-end delivery and can transform data across multiple links.
  • The Network Layer receives services from the Transport Layer and provides services to the Data Link Layer.
  • Layered model: Transport Layer

Page 11

  • Addressing:
    • Every computer on the Internet has a unique Internet Address (IP address).
    • IPv4 addresses are 32-bit and used to identify hosts/routers for Internet connectivity.
    • IP addresses appear in the IP header in the Source and Destination fields.
    • Representations of IP addresses can be: Binary (base 2), Dotted decimal (base 10), and Hexadecimal (base 16).

Page 12

  • IPv4 Address Format:
    • A 32-bit IP address consists of two parts: NetID (network identifier) and HostID (host within the network).
    • IPv4 address classes: A, B, C, D, E.
    • Class A: first octet ranges 1–127; NetID = 8 bits, HostID = 24 bits; Example: 10.0.0.0/8.

Page 13

  • Class B format:
    • Range: 128-191 (first octet).
    • Network/Host composition: NetID and HostID bits as specified for Class B (commonly 16 network bits, 16 host bits in standard practice; transcript mentions 10 and 14 bits).
    • Use: Medium-sized networks.
    • Example: 172.16.0.0/16.

Page 14

  • Class C format:
    • Range: 192-223 (first octet).
    • NetID = 24 bits; HostID = 8 bits (standard Class C).
    • Use: Smaller networks; Example: 192.168.0.0/24.
  • Class D format:
    • Range: 224-239; Multicasting.
    • Example: 224.0.0.0/4 (multicast address).
  • Class E format:
    • Range: 240-255; Reserved for future use.

Page 15

  • Default subnet masks (classful addressing):
    • Class A: 255.0.0.0
    • Class B: 255.255.0.0
    • Class C: 255.255.255.0
  • Subnetting: dividing a larger network into smaller, isolated subnets.
  • Subnet: logical subdivision of an IP address.
  • Supernetting: combining multiple smaller IP ranges into a single larger contiguous range.

Page 16

  • NAT (Network Address Translation):
    • Allows multiple devices on a private network to share a single public IP address when accessing the Internet.
    • Example mapping: Private 174.122.1.1 -> Public 244.46.1.1.
  • Purpose of NAT:
    1) IP address conservation
    2) Security
    3) Network flexibility
    4) Help with overlapping/private address usage
    5) Information transfer (as implied by transcript)

Page 17

  • IP header and network-layer details:
    • IP is host-to-host delivery protocol at the Network Layer.
    • Header fields include: Version, IHL, Service, Total Length, Identification, Flags, Fragment Offset, TTL, Protocol, Header Checksum, Source IP Address, Destination IP Address, Options, Padding.
    • IP is primarily for unicast delivery; multicast requires additional protocol support (transcript mentions JUMP as the multicast helper).

Page 18

  • IPv6 overview:
    • IPv6 is the successor to IPv4, designed to replace IPv4 for addressing and routing.
    • Advantages: simpler header, larger address space, better security, plug-and-play, improved scalability, IoT support, and overall efficiency.
  • Need for IPv6:
    • Enhanced security features
    • Improved network efficiency
    • Support for Internet of Things (IoT)
    • Future-proofing the network

Page 19

  • Difference between IPv4 and IPv6:
    • Address size: IPv4 is 32-bit; IPv6 is 128-bit.
    • Address formats: IPv4 uses dotted decimal; IPv6 uses hexadecimal colon notation.
    • Address types: IPv4 supports unicast, multicast, and broadcast; IPv6 supports unicast and multicast (broadcast is not used).
    • Header size: IPv4 header is smaller (20 bytes typical) versus IPv6 header (40 bytes).

Page 20

  • Network Layer Protocols:
    • IP provides logical addressing, routing, and forwarding.
    • ICMP handles control messages for network diagnostics and error reporting.
    • ARP resolves IP addresses to MAC addresses.
    • For multicast, IP uses additional protocols (transcript mentions JUMP as the multicast helper).

Page 21

  • Address Resolution Concepts:
    • IP addresses are essential for end-to-end communication; hardware addresses (MAC) operate at the link layer.
    • Common address types include: Static and Dynamic (for IP assignment); other address types exist but are not detailed in the transcript.
    • MAC addresses are used by the data link layer, while IP addresses are used by the network layer.

Page 22

  • ARP (Address Resolution Protocol):
    • Purpose: map a given IP address to its MAC (hardware) address on a local network.
    • How it works: a device broadcasts an ARP request asking who has a specific IP; the device with that IP responds with its MAC address; the requester caches this mapping in its ARP cache for future use.

Page 23

  • ARP operations (process):
    • ARP Request: broadcast to all devices on the network.
    • ARP Response: unicast to the requester with the MAC address.

Page 24

  • RARP (Reverse Address Resolution Protocol):
    • Purpose: map a device's MAC address to its IP address; useful for diskless machines that cannot store an IP address.
    • Advantages: simplified device configuration; reduced overhead; support for legacy devices.
    • Disadvantages: server location limitation; not forwardable by routers; lack of subnetting support; not suitable for modern networks.

Page 25

  • Differences: ARP vs RARP
    • ARP: resolves IP address to MAC address.
    • RARP: resolves MAC address to IP address (learns its own IP).
    • ARP operation codes (RFC 826): 1 = request, 2 = reply.
    • RARP operation codes (per transcript): 3 = request, 4 = reply.
    • ARP cache is maintained by the local host; RARP is typically served by a RARP server to configure/learn IP.