The Network and Transport Layers

CHAPTER 5 The Network and Transport Layers

Learning Objectives

• Differentiate between the standards, specifications, technologies, and infrastructure that drive current LAN connectivity.

Key Concepts

• The Network and Transport Layers of the OSI model

• Internet Protocol (IP)

• IP Device Addressing:

  • Using IPv4 and IPv6.

• IP-based Communications:

  • Connectionless versus connection-oriented communications.

OSI Model Overview

• Figure 5-1: Comparison of the OSI model to the TCP/IP model.

Knowledge Check 1

• Question: True or False: the term "router" is synonymous with a Layer 2 switch.

OSI Layers

The OSI Network Layer (Layer 3)

• Provides network addressing for packets.

• Supports switching and routing technologies to direct packets.

• Addresses issues related to packet delivery from source to destination.

• Supports the creation of virtual circuits.

• Protocols at OSI Layer 3 include:

  • Internet Protocol (IP): The main protocol for transmitting packets across networks.

  • Internet Control Message Protocol (ICMP): Provides methods to send error messages.

  • Internet Protocol Security (IPSec): For authentication and encryption of packets.

  • AppleTalk: A legacy protocol now replaced by TCP/IP.

Knowledge Check 2

• Question: Which protocol guarantees delivery? TCP or UDP?

The OSI Transport Layer (Layer 4)

• Ensures reliable data transfer between computers.

• Accepts data from upper layers.

• Services provided include:

  • Flow control to manage transmission pace.

  • Fragmentation and reassembly of data packets.

  • Error control to detect missing packets.

  • Acknowledgment of delivery to ensure packets have arrived.

• Protocols at Layer 4 include:

  • Transmission Control Protocol (TCP): Used for applications like WWW and email; persistent connection.

  • User Datagram Protocol (UDP): Faster, less overhead; used in applications like DNS.

  • Stream Control Transmission Protocol (SCTP).

Knowledge Check 3

• Question: Which of the following network devices operates at Layer 3 of the OSI model?

  • 1. Switch

  • 2. Router

  • 3. Hub

  • 4. Bridge

Internet Protocol (IP)

• Primary protocol for relaying packets across networks.

• Handles packet routing and host identification.

• Each packet, or datagram, contains a header with the destination IP address.

IPv4 and IPv6 Packet Headers

• IPv4 Packet Header:

  • Figure 5-3: Structure of an IPv4 packet header.

• IPv6 Packet Header:

  • Figure 5-4: Structure of an IPv6 packet header.

Decentralization of IP Protocol

• IP networks are decentralized and dynamic.

• Packets may not reach the intended destination.

• Checksums can detect changes in packet headers.

Knowledge Check 5

• Question: True or False: IP provides automatic notification of lost packets.

Checksum in IPv4

• Figure 5-6: Demonstrates IPv4 header checksum usage.

Knowledge Check 6

• Question: Which protocol includes a checksum to ensure data integrity? (Options: IP, TCP, UDP, All of the above)

Knowledge Check 7

• Question: What do you remember about IPv4 and IPv6?

IP Addressing: IPv4 vs IPv6

• Devices require IP addresses for IP-based networks.

• Internet Assigned Numbers Authority (IANA): Governs IP address allocation.

• IPv4 is largely used despite the transition to IPv6.

• IPv4:

  • 32-bit addresses presented in dot notation (e.g., 192.168.0.1).

  • Classful and classless networks exist.

• Dynamic Host Configuration Protocol (DHCP): Assigns IP addresses dynamically.

• Network Address Translation (NAT): Allows private IP address use.

Knowledge Check 8

• Question: Why do organizations choose to separate their DHCP server from a router or firewall?

IPv4 Classful Network Architecture

• Original architecture with classes for addressing: Classes A, B, C, D, E.

  • Class A: 0 leading bits, allows large number of nodes.

  • Class B and C serve medium and small networks respectively.

Classful Network Classes Table

CIDR and Subnet Mask in IPv4

• CIDR (Classless Inter-Domain Routing): Aids in addressing shortage, replaces classful architecture.

• Subnet Masks: Define which portion of an IP address is the network versus the host.

CIDR Block Addresses Table

Subnet Masks Table

Address Resolution

• Process of mapping hostnames to IP addresses.

• Domain Name System (DNS): Hierarchical system to resolve hostnames.

IPv6 Overview

• Created to expand the address space; it uses 128-bit addresses.

• IPv6 Format: Eight groups of four hexadecimal numbers.

Knowledge Check 11

• Question: What is the bit size of IPv4 versus IPv6? (Options: 128; 32, 32; 128)

IPv6 Address Compression

• Techniques to simplify IPv6 addresses by dropping leading zeros and using :: for sequences of 0s.

IPv6 Network Methodologies

• Unicast: Packet sent to one destination.

• Anycast: Packet sent to the nearest node in a group.

• Multicast: Packet sent to multiple destinations.

• Note: IPv6 does not support broadcast packets.

IPv4 to IPv6 Transition

• Dual IP stack allows support of both IPv4 and IPv6.

• IPv4-mapped addresses enable IPv6 to utilize IPv4 addresses.

IP Communications

• ARP in IPv4 networks provides MAC addresses while IPv6 uses Neighbor Discovery Protocol (NDP).

• Support for various data types over IP networks including emails, calls, and streaming data.

Connectionless vs Connection-Oriented Communications

• IP as Connectionless Protocol: Treats each packet independently.

• Connection-Oriented Protocols (e.g., TCP): Establish connections and manage data transfer order.

Connection-Oriented vs Connectionless Protocols

• Figure 5-8: Visual comparison of connection-oriented and connectionless protocols.

TCP (Transmission Control Protocol)

• Connection-oriented; more setup work than UDP.

UDP (User Datagram Protocol)

• Connectionless; suitable for simple queries and load balancing.

• Other connectionless protocols include: ICMP, DNS, TFTP, SNMP.

Summary

• Covered the Network and Transport Layers of the OSI model, IP addressing with IPv4 and IPv6, and the differences between connectionless and connection-oriented communications.