Root dns server

As explained in Acing the CCNA Exam: Volume 2 Advanced Networking and Security

A root DNS server is a DNS server at the top of the DNS hierarchy that directs queries toward the appropriate top-level domain servers.

A root DNS server sits at the top of the DNS hierarchy and guides iterative resolution when a recursive resolver lacks a cached answer. It does not normally return the requested IP address; instead, it refers the resolver to the relevant top-level domain (TLD) server. section 3.1.4

During resolution, the sequence is:

• A client sends a recursive query requesting a definite answer to its recursive resolver. section 3.3
• The recursive resolver sends an iterative query to a root server. section 3.1.4
• The root server refers the resolver to the server responsible for the queried TLD, such as com. section 3.1.4
• The TLD server then refers the resolver to the domain’s authoritative DNS server, which supplies the definitive record. section 3.3

Figure 3.4 Recursive and iterative DNS requests resolve a domain name. In step 1, PC1 attempts to access mail.google.com. Steps 2 and 9 are a recursive DNS exchange between PC1 and the 8.8.8.8 DNS server. Steps 3 through 8 are iterative DNS exchanges between 8.8.8.8 and other DNS servers. Step 10 is an HTTPS exchange between PC1 and mail.google.com.

Follow the complete exchange: recursive requests connect the client and resolver, while iterative requests connect the resolver with root, TLD, and authoritative servers. section 3.1.4

How Acing the CCNA Exam: Volume 2 Advanced Networking and Security covers it

How deep it goes

Explains iterative referrals through root, TLD, and authoritative servers, while stopping short of server configuration.

Examples

Uses mail.google.com and 8.8.8.8 to demonstrate root-to-TLD referral during an uncached lookup.

What it assumes

Assumes familiarity with DNS queries, domain-name hierarchy, recursive resolvers, and authoritative servers.

What you can do after

Evaluate DNS resolution by distinguishing recursive client queries from iterative resolver-to-server referrals.

How it connects

Connects recursive queries, recursive resolvers, TLD servers, authoritative DNS servers, caching, and DNS records.

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Related concepts

• DNS serverused by · A DNS server is a network service that answers domain-name queries by returning corresponding DNS records or obtaining them from other DNS servers.
• tld serveruses · A TLD server is a DNS server responsible for a top-level domain that directs queries to authoritative servers for domains within it.
• root domainuses · A root domain is the highest-level domain in a domain-name hierarchy, from which subordinate domains are organized.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 2 Advanced Networking and Security. The section links point to the parts of the book it draws on.