networking recap 1

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Recap of Previous Lecture

The instructor mentions a continuation from the last lecture, emphasizing the importance of understanding the fundamentals of computer networking for IT 404. Key points from the previous lecture include:

OSI Layers Overview

  • Physical Layer: Discussed as the foundational layer in OSI.

  • Data Link Layer: Covered MAC addresses and their use in multi-hop setups.

  • Network Layer: Focus on the Internet Protocol (IP) addresses and their necessity in conjunction with MAC addresses in multi-hop networks.

  • Transport Layer:

    • Discussed TCP, including its three primary services:

    1. End-to-End Reliability: Ensures that messages are delivered accurately and in order.

    2. Congestion Control: Manages data flow to prevent network overload.

    3. Segmentation of Data: Breaks down larger messages into manageable segments.

    • Introduced UDP as a simpler transport option that does not offer the same reliability features as TCP.

Session Layer

  • Discussed the concept of the session layer within the OSI model:

    • Merging with the transport layer in actual Internet implementations.

    • Utilizes two port numbers (source port number and destination port number) to manage sessions.

  • Key Details on Port Number:

    • Both source and destination port numbers are allocated 2 bytes each within TCP and UDP.

    • The number range for port numbers is from 0 to 65535 (though 0 has a specific meaning as a request to not reply).

Introduction to New Networking Concepts

Transitioning into new material, the instructor sets to discuss the various layers and protocols involved in networking:

Key Concepts & Protocols:

  • Ports (0-1024):

    • Known as well-known ports reserved for specific protocols.

    • Importance of these port numbers in common protocols will be made clearer throughout the lecture.

Presentation Layer

  • Key role in network infrastructure, particularly in end-to-end encryption.

  • Notable protocols:

    • TLS: Provides encryption for transactions.

    • SSL: Older standard for encryption, with TLS now considered more secure and common.

Application Layer

  • Highly interactive layer where most web development occurs. Notable protocols include:

    • HTTP:

    • Most significant for web transmission. Demonstrated as having plain versions (HTTP) and encrypted versions (HTTPS).

    • HTTPS indicates HTTP over TLS security.

    • FTP: Used for file transfer.

    • SSH and Telnet: For remote command execution, with SSH being encrypted.

    • SMTP: For email exchange.

DNS (Domain Name System)

  • Essential service for translating domain names into IP addresses. Explained as:

    • DNS = A "quality of life" service, allowing users to remember text-based domain names instead of numeric IP addresses.

    • Client-Server Model: The client (user machine) communicates with a DNS resolver to obtain the appropriate IP address for a requested domain.

DNS Resolution Process

  • When a DNS request is made (e.g., for "google.com"), the resolver queries the root DNS server to obtain the IP address of the DNS server responsible for the .com domain, then proceeds to query the corresponding DNS server for google.com.

  • Caching Mechanism: Improves speed, where once a query is made, subsequent requests for the same address can be answered from cache rather than requiring the entire resolution process again.

  • Reverse DNS Lookup: An additional function where an IP can also be translated back into a domain name.

Detailed Explanation of how DNS Uses UDP

  • Default DNS configuration predominantly relies on UDP to transmit requests because it allows for faster communication without requiring a three-way handshake like TCP, thus operating quicker and more efficiently for the usual single-request nature of DNS queries.

  • If a request does not receive a response, it can be re-sent without the procedural wait imposed by TCP’s handshake.

Domain Name Hierarchy Overview

  • The instructor covers the domain name system's hierarchy:

    • Root Servers: Top-level entities that direct queries to TLD (Top Level Domain) servers (e.g., .com, .org), which then direct to specific domain servers (like google.com).

    • Caching: Relies heavily on the Time-to-Live (TTL) attribute, deciding how long DNS records are kept before being re-queried.

Transitioning to Domain Registration

  • Stress on the necessity of registering domain names through a registrar:

    • Domain names are effectively rented, requiring renewal at least annually.

  • Discusses online tools for searching and securing domain names through various registrars,

  • Provides insights into potential pitfalls in renewal pricing where the initial price may be attractive but could increase upon renewal.