2.4 The Domain Name System (DNS)

Summary

This video script delves into the Domain Name System (DNS), a critical component of the internet that translates human-readable host names into IP addresses. It explores DNS as an application layer protocol built on TCP/UDP, emphasizing its distributed nature, hierarchy of servers, and functions like aliasing and load balancing. The script explains DNS records, message formats, and the importance of caching. It also touches on DNS security, highlighting the need for protection against attacks and data authentication.

Takeaways

• 🌐 The DNS (Domain Name System) is a critical part of the internet that translates human-friendly host names into IP addresses.
• 🔍 DNS operates at the application layer, using TCP and UDP protocols to provide its services.
• 📚 DNS is a distributed database with a hierarchy of servers, including root, TLD (Top-Level Domain), authoritative name servers, and local DNS servers.
• 🔄 The DNS resolution process can involve iterative or recursive queries, with iterative queries being more common due to their efficiency.
• 🏢 DNS provides various functions, including IP address to host name translation, aliasing, service resolution, and load balancing.
• 🌟 DNS is designed to be highly scalable and performant, handling trillions of requests daily with low latency.
• 🛡️ Security is paramount for DNS, with measures in place to prevent denial of service attacks and ensure data authenticity.
• 💾 DNS records are stored as four-tuples, including name, value, type, and TTL (Time to Live), with common types being A, NS, CNAME, and MX records.
• 📈 DNS caching is used to improve response times and reduce load on the DNS infrastructure by temporarily storing resolved queries.
• 🌱 To establish an internet presence, a company must register a domain name, obtain IP addresses, and set up an authoritative DNS server with resource records.

Q & A

What is the primary function of DNS?

The primary function of DNS is to translate human-friendly domain names, such as gaia.cs.umass.edu, into IP addresses, such as 128.119.40.186, which computers use to identify each other on the internet.

Why is DNS considered an application layer protocol and service?

DNS is considered an application layer protocol and service because it is built on top of and uses the services of TCP and UDP, which are transport layer protocols, to perform its name translation services.

What are the different functions provided by DNS?

DNS provides several functions including IP address to host name translation, aliasing to translate externally facing names to internal hostnames, service resolution to return the IP address of a mail server associated with a domain, and load balancing by rotating among multiple IP addresses for a requested service.

Why is a decentralized approach used for DNS rather than a centralized one?

A decentralized approach is used for DNS to avoid a single point of failure, to prevent a concentration of traffic that could compromise performance, and to ensure scalability and resilience, which are critical given the massive scale of DNS queries.

What is the role of root DNS servers in the DNS hierarchy?

Root DNS servers are the starting point for DNS resolution when a local DNS server cannot resolve a name. They provide the initial reference to Top-Level Domain (TLD) servers, which are responsible for domains like .com, .edu, or .net.

How does the DNS caching mechanism work and why is it important?

DNS caching works by storing the mappings of hostnames to IP addresses for a certain period of time, known as Time to Live (TTL). This is important because it reduces the number of queries to DNS servers, improves response time, and takes load off the DNS infrastructure.

What is the difference between iterative and recursive query resolution in DNS?

Iterative query resolution involves the local DNS server querying a sequence of servers until the name is resolved, while the recursive query resolution places the burden on the servers at the upper level of the hierarchy, where one server takes responsibility for resolving the query and returning a definitive reply.

What are the four components of a DNS database record?

A DNS database record is a four tuple consisting of the name, value, type, and TTL (Time to Live). The type indicates the kind of record, such as an A record for IP address, an NS record for name server, a CNAME record for aliasing, or an MX record for mail server.

How does the DNS protocol message format look like for both query and reply messages?

Both query and reply messages in DNS have the same format, which includes fields for ID, flags, number of questions, number of answers, and resource records. The ID field is chosen by the querier and is used to match responses with queries, while the flags indicate whether it's a query or reply and other status information.

What steps are required to establish an internet presence for a new company using DNS?

To establish an internet presence, a company needs to register its domain name with a DNS registrar, obtain a range of IP addresses for its servers, provide the name and address of its authoritative name server to the registrar, and set up the authoritative name server with resource records for the network's servers.