DNS Protocol and Attacks

published: February 11, 2025
reading time: 9 minutes

DNS Protocol & Attacks

Introduction

What is DNS?

DNS Stands for Domain Name System

DNS (Domain Name System):
- Translates human-friendly domain names (e.g., www.amazon.com, www.netflix.com) into numeric IP addresses that computers use to identify each other on the Internet.
The Human vs. Computer Paradigm:
- Humans can easily remember domain names, while computers rely on numeric IP addresses (e.g., IPv4 like 51.23.8.9 or IPv6 like 2400:CB00:2048:1::C629:D782).
DNS as the Internet’s Phonebook:
- Functions similarly to a phonebook by allowing users to look up a domain name and retrieve the corresponding IP address.
- Eliminates the need for humans to memorize or manually input complex IP addresses.
Critical Role in Internet Functionality:
- Enables everyday tasks such as online shopping, banking, and streaming by seamlessly connecting domain names to the correct servers.
- Without DNS, the usability of the Internet as we know it would be significantly diminished.
Beyond Basic Name Resolution:
- While the basic function of DNS is to translate names to IP addresses, its underlying architecture is more sophisticated and versatile.
- Further course content will explore these complexities in greater detail.

The main Function if DNS

Three Main Functions of DNS:
- Name Resolution:
  - Translates domain names into IP addresses.
  - This is the core function of DNS.
- Namespace:
  - Defines how domain names are structured.
  - Determines what makes a name valid, including the format and allowed characters/symbols.
  - Explains how names are interpreted.
- Name Registration:
  - Involves the process of registering a domain.
  - Ensures the uniqueness of domain names.
  - Details the role of registration authorities in the name assignment process.
Complexity and In-Depth Study:
- Each of these areas (name resolution, namespace, and name registration) is broad and detailed.
- The course is structured to dedicate a section to each function to explore them fully, starting with namespace.

Name Space

Domain Name Format

Introduction:
- Covers the breakdown of a typical domain name into individual components.
- Emphasizes that this lecture lays the foundational knowledge for understanding DNS namespaces.
- Recommendation for beginners: watch the video more than once and take detailed notes.
Domain Name Interpretation Direction:
- Although we type domain names from left to right, DNS interprets them from right to left.
Components of a Domain Name (from Right to Left):
- Root (Special Dot):
  - Represented by a unique, dominant dot at the far right.
  - This dot is distinct (often colored differently) and serves as the ultimate terminator of a domain name.
- Top-Level Domain (TLD):
  - Follows immediately after the root.
  - Example given: .com (others include .net, .org, .io, etc.).
  - Combined with the second-level domain, it forms the zone apex (or naked/apex domain).
- Second-Level Domain (SLD):
  - In the example, this is example.
  - Along with the TLD, it makes up the main, recognizable part of the domain.
- Third-Level Domain:
  - Commonly used as www, but it’s simply a naming convention and can be replaced by any arbitrary string.
- Labels:
  - Each part (root, TLD, SLD, etc.) is known as a label.
  - Each label is a subdomain of its parent domain.
  - The entire sequence of labels from the root up forms the Fully Qualified Domain Name (FQDN), which is the absolute reference to a domain.
Domain Name vs. URL:
- Domain Name: Only the name component (e.g., www.example.com).
- URL: Includes additional components such as the protocol (e.g., https://) and path (e.g., /learning).
Partially Qualified Domain Name (PQDN):
- A domain name that includes the hostname but does not extend all the way to the root.
Syntax Rules for Domain Names:
- Label Length: Each label can be up to 63 characters long.
- Allowed Characters: Letters (a–z, A–Z), digits (0–9), and hyphens.
  - This is referred to as the LDH rule.
  - Labels cannot begin or end with a hyphen.
- TLD Restrictions: Top-level domains should not be entirely numeric.
- Subdomains: There is no maximum limit on the number of subdomains.
- Overall Length: A complete domain name can be up to 255 characters, including dots.
Conclusion:
- Recap of the domain name components and syntax.
- Transition note: This lecture sets the stage for deeper discussions in later parts of the course.

The DNS Tree

Introduction:
- Recap of domain name composition.
- Transition into understanding the context in which domain names exist.
DNS vs. Phonebook Analogy:
- Similarities:
  - Both map names to numbers (e.g., DNS maps domain names to IP addresses; a phonebook maps names to telephone numbers).
- Differences in Structure:
  - A phonebook is a single, centralized authority covering a specific geographic region.
  - A central database approach (flat name architecture) is used in a phonebook, which doesn’t scale well for the entire Internet.
Challenges with Flat Name Architecture:
- Administrative Overhead:
  - Managing every possible domain name in a central database would be extremely demanding.
- Scalability Issues:
  - Flat systems do not scale well to handle hundreds of thousands (or millions) of devices.
- Uniqueness Guarantee:
  - It is extremely difficult to ensure that every domain name is unique across a flat namespace.
Adoption of Hierarchical Name Architecture:
- Rationale:
  - To overcome the limitations of a flat architecture, DNS uses a multi-level hierarchical structure.
- Structure:
  - The Internet is organized as a globally distributed collection of databases that form a tree-like structure.
  - Each domain name represents a path in this tree.
- Decentralized Administration:
  - Authority is delegated to various organizations.
  - Each organization manages its own domain data and can further subdivide into subdomains.
  - This delegation supports scalability and simplifies management.
Benefits of the Hierarchical Model:
- Decentralized Administration:
  - No single entity manages the entire namespace.
- Management Flexibility:
  - Organizations can manage and delegate subdomains, allowing the namespace to grow organically with the Internet.
- Uniqueness:
  - The hierarchical structure helps guarantee that every domain name is unique across the global Internet.
DNS Infrastructure Overview:
- Components:
  - Root Name Servers: Sit at the top of the hierarchy.
  - Top-Level Domain (TLD) Name Servers: Follow the root servers.
  - Authoritative Name Servers: Provide the final mapping to IP addresses.
- Next Steps:
  - The next lecture will focus on studying the root name servers and their critical role in the DNS namespace.

Root Servers

Introduction to Root Servers:
- Recap of DNS’s role in translating domain names into IP addresses (name resolution).
- Introduction to the concept of “roots” within the DNS hierarchy.
Role and Function of Root Servers:
- First Point of Contact:
  - Root servers are the first component in the DNS tree that receive a DNS query.
- Referral Process:
  - Upon receiving a query, a root server provides a referral to the appropriate top-level domain (TLD) name server based on the domain extension.
  - Example: For www.yahoo.com, the root server passes the query to a TLD server corresponding to .com.
Understanding the Query Process:
- The conversion of a domain name to an IP address (name resolution) starts with a query that is first directed to a root server.
- Additional systems and background technologies work before a query reaches a root server, as indicated by visual cues (like square brackets with dots) in the presentation slides.
Key Details About Root Servers:
- Number and Naming:
  - There are 13 root name servers, each identified by letters A through M.
- Further Information:
  - Detailed data about these servers—including operators, physical locations, IP and IPv6 addresses, and related autonomous system numbers (associated with the BGP protocol)—is available at root-service.org.
- Infrastructure Scale:
  - Although there are 13 designated servers, there are multiple physical copies (over 130 locations worldwide) to manage high traffic loads.
  - As of February 20, 2019, there were 938 operational root server instances globally.
Conclusion:
- Root servers play a critical role in the DNS resolution process.
- A deeper understanding of root servers and their role will be built upon in later discussions on name resolution.

TLD Servers

Role in DNS Resolution:
- Transition from Root Servers:
  - After a DNS query reaches a root server and receives a referral, the query is passed to a TLD nameserver.
- Primary Function:
  - The TLD nameserver’s job is to provide its own referral pointing to an authoritative nameserver that has authority over the requested domain (e.g., Yahoo).
Hierarchical Architecture:
- Distributed Databases:
  - Unlike a flat architecture with a single central database, DNS uses a hierarchical system where each branch holds only part of the necessary information.
- Step-by-Step Resolution:
  - Each level in the DNS hierarchy (root, TLD, and authoritative) contributes a piece of the puzzle needed to fully resolve a domain name.
Categories of Top-Level Domains:
- Generic Top-Level Domains (gTLDs):
  - Reflect the type of organization or industry (e.g., .com, .edu).
  - Example: Government agencies typically use .gov, and universities use .edu.
  - The original gTLDs included domains like .arpa, .com, and .net; newer ones like .aero and .pro have also been added.
- Country Code Top-Level Domains (ccTLDs):
  - Allow countries to manage their own namespace and cater to local languages and needs.
  - Examples include Japan’s .jp, Greece’s .gr, Italy’s .it, and Poland’s .pl.
  - Countries may also use organizational subdomains within their ccTLDs (e.g., the UK uses .co.uk for companies, and Australia uses .com.au).
Additional TLD Categories:
- Other specialized TLD categories exist beyond gTLDs and ccTLDs; however, these are outside the scope of this course.
- For a complete list of TLDs, refer to the IANA website at:
  https://www.iana.org/domains/root/db
Conclusion and Next Steps:
- The TLD nameserver plays a crucial role by passing back a referral to the authoritative nameserver for the requested domain.
- The next lecture will continue the journey by explaining how the query reaches and is handled by the authoritative nameservers.

Authoritative Name Servers

Introduction to Authoritative Name Service:
- Marks the final component of the DNS namespace section.
- Focuses on the role of the authoritative name server in completing the DNS resolution process.
Understanding Authority in DNS:
- Definition of Authority:
  - In DNS, a domain represents a sphere of influence governed by an entity responsible for managing that portion of the namespace.
  - Authority implies responsibility for providing accurate DNS data (e.g., IP addresses) for that segment.
- Analogies:
  - Like a medieval lord governing a territory or an expert being the leading authority in a field, an entity in DNS manages a specific domain.
- Hierarchical Nature:
  - The DNS namespace is divided into segments, each managed by a designated authority.
  - A single authority can manage multiple levels of the hierarchy (e.g., ICANN manages both the root and TLD segments).
Role of the Authoritative Name Server:
- DNS Resolution Process:
  - Initial queries are handled by root servers and then TLD (Top-Level Domain) servers.
  - Both the root and TLD servers provide referrals because they are not authoritative for specific domains (e.g., www.youtube.com).
- Final Step:
  - The authoritative name server holds the definitive DNS records for a domain.
  - It completes the resolution process by returning the final answer (the IP address) for the requested domain (e.g., www.yahoo.com).
- No Further Referrals:
  - Unlike previous steps, once the query reaches the authoritative server, there is no further referral—just the final response.
Delegation and Management within the DNS Hierarchy:
- Organizations (like ICANN) can manage broad segments (e.g., the root or an entire top-level domain).
- Domain owners can delegate authority over subdomains to other organizations.
  - Example: As the owner of securitycharms.com, you might delegate management of a subdomain (e.g., sub.securitycharms.com) to another entity.
Course Recap and Next Steps:
- Topics Covered in the Namespace Section:
  - Definition of DNS and its primary functions.
  - The DNS tree structure and domain name syntax.
  - The roles of root servers, TLD servers, and authoritative name servers.
- Progress Acknowledgment:
  - With this lecture, you’ve reached an intermediate level of understanding.
- Looking Ahead:
  - The course will continue with a focus on the name resolution process in greater detail.