Short Notes: Network Layer | Computer Networks - Computer Science Engineering (CSE) PDF Download

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1 Network Layer in Computer Networks
1.1 Introduction to Network Layer
TheNetworkLayer(Layer3intheOSImodel)isresponsibleforthesource-to-destination
deliveryofpacketsacrossmultiplenetworks. Itensurespacketsareroutedfromthesender
tothereceiver,evenwhentheytraversedi?erentnetworks,byprovidinglogicaladdressing
and path determination.
1.2 Functions of Network Layer
• Logical Addressing: Assigns unique IP addresses to distinguish source and des-
tination systems across networks.
• Routing: Determines the optimal path for packet forwarding using routers or
gateways, connecting independent networks.
• PacketForwarding: Transferspacketsfromsourcetodestination, possiblyacross
multiple network links.
• Fragmentation and Reassembly: Divides packets into smaller fragments for
transmission and reassembles them at the destination.
• Error Reporting: Uses protocols like ICMP to report issues such as unreachable
hosts or network congestion.
1.3 Internet Protocol (IP)
• IPv4: Uses 32-bit addresses (e.g., 192.168.1.1), divided into classes (A, B, C, D,
E) for addressing and routing.
• IPv6: Uses 128-bit addresses to support more devices, with enhanced features like
simpli?ed headers and better security.
• IP ensures connectionless, best-e?ort delivery of packets (datagrams).
1.4 IP Addressing Example: Class A
• Range: 0.0.0.0 to 127.255.255.255 (?rst octet: 0127).
• Structure: 1 octet for network ID, 3 octets for host ID.
• Example: 10.1.2.3 (network: 10.0.0.0, host: 1.2.3).
• Supports large networks with up to 16 million hosts.
1.5 Key Protocols
• Address Resolution Protocol (ARP): Maps IP addresses to MAC addresses
for local network communication.
• Dynamic Host Con?guration Protocol (DHCP): Automatically assigns IP
addresses and network con?guration to devices.
• Internet Control Message Protocol (ICMP): Handles error reporting and
diagnostics (e.g., ping, destination unreachable).
• OpenShortestPathFirst(OSPF):Alink-stateroutingprotocolthatcalculates
the shortest path for packet routing within an autonomous system.
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1 Network Layer in Computer Networks
1.1 Introduction to Network Layer
TheNetworkLayer(Layer3intheOSImodel)isresponsibleforthesource-to-destination
deliveryofpacketsacrossmultiplenetworks. Itensurespacketsareroutedfromthesender
tothereceiver,evenwhentheytraversedi?erentnetworks,byprovidinglogicaladdressing
and path determination.
1.2 Functions of Network Layer
• Logical Addressing: Assigns unique IP addresses to distinguish source and des-
tination systems across networks.
• Routing: Determines the optimal path for packet forwarding using routers or
gateways, connecting independent networks.
• PacketForwarding: Transferspacketsfromsourcetodestination, possiblyacross
multiple network links.
• Fragmentation and Reassembly: Divides packets into smaller fragments for
transmission and reassembles them at the destination.
• Error Reporting: Uses protocols like ICMP to report issues such as unreachable
hosts or network congestion.
1.3 Internet Protocol (IP)
• IPv4: Uses 32-bit addresses (e.g., 192.168.1.1), divided into classes (A, B, C, D,
E) for addressing and routing.
• IPv6: Uses 128-bit addresses to support more devices, with enhanced features like
simpli?ed headers and better security.
• IP ensures connectionless, best-e?ort delivery of packets (datagrams).
1.4 IP Addressing Example: Class A
• Range: 0.0.0.0 to 127.255.255.255 (?rst octet: 0127).
• Structure: 1 octet for network ID, 3 octets for host ID.
• Example: 10.1.2.3 (network: 10.0.0.0, host: 1.2.3).
• Supports large networks with up to 16 million hosts.
1.5 Key Protocols
• Address Resolution Protocol (ARP): Maps IP addresses to MAC addresses
for local network communication.
• Dynamic Host Con?guration Protocol (DHCP): Automatically assigns IP
addresses and network con?guration to devices.
• Internet Control Message Protocol (ICMP): Handles error reporting and
diagnostics (e.g., ping, destination unreachable).
• OpenShortestPathFirst(OSPF):Alink-stateroutingprotocolthatcalculates
the shortest path for packet routing within an autonomous system.
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1.6 Routing Mechanisms
• Static Routing: Manually con?gured routes, suitable for small, stable networks.
• DynamicRouting: UsesprotocolslikeOSPForBGPtoadapttonetworkchanges
dynamically.
• Routers maintain routing tables to determine the best path for packets based on
destination IP addresses.
1.7 Hardware Used
• Routers: Forward packets between networks based on IP addresses.
• Gateways: Connect dissimilar networks, often performing protocol translation.
1.8 Data Unit
• Packets: The Network Layer encapsulates data into packets, each containing
source and destination IP addresses.
1.9 Short Questions and Answers
1. What is the primary role of the Network Layer? It ensures source-to-
destination packet delivery across multiple networks.
2. How does ARP function? ARP resolves IP addresses to MAC addresses for
communication within a local network.
3. What is the di?erence between IPv4 and IPv6? IPv4 uses 32-bit addresses,
while IPv6 uses 128-bit addresses with improved scalability and security.
4. WhyisOSPFused? OSPF dynamically calculates the shortest path for routing,
adapting to network topology changes.
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