DNS Resolution Walkthrough

About this interactive

A DNS lookup is the most-described process in networking and one of the least understood, because the description usually stops at a diagram with four boxes and three arrows. The details a troubleshooting question turns on are the ones the diagram leaves out: the root server answers with a referral rather than an address, and refers only to .com — never straight to the domain; the TLD server ships the nameserver's ADDRESS as a glue record because the nameserver lives inside the zone you have not reached; the authoritative answer is marked as such in a header bit, which is the only reason the walk knows to stop; the client sent exactly one query out of the four; and the TTL that arrives with the answer is set by the zone owner, counts down rather than resetting, and cannot be revoked once the answer has left. This activity walks one real resolution and asks you to predict each of those before it shows you.

What you'll learn

Trace a single DNS query through the hosts file, a recursive resolver, a root server, a TLD server and an authoritative nameserver, naming what each tier can and cannot answer
Distinguish a recursive query from an iterative one, and a referral from an authoritative answer, and identify which party sends each
Predict what a resolver and a client cache after a resolution, how long they hold it, and what an unexpired TTL does to a record change that has already been made

Aligned to

CompTIA Network+

1.4 Explain common networking ports, protocols, services, and traffic types.

3.4 Given a scenario, implement IPv4 and IPv6 network services.

Cisco CCNA

4.3 Explain the role of DHCP and DNS within the network.

Cisco CCST Networking

1.5 Describe common network applications and protocols.

CompTIA A+ Core 1

2.6 Compare and contrast common network configuration concepts.

Key terms

Domain Name System: A hierarchical naming system that translates human-readable domain names into IP addresses.
Root Server: A DNS server at the top of the DNS hierarchy that responds to queries by directing resolvers to the appropriate top-level domain server.
Top-Level Domain: The last segment of a domain name, such as .com, .org, or .net, representing the highest level of the DNS hierarchy.
Authoritative Name Server: A DNS server that holds the definitive DNS records for a specific domain and provides the final IP address answer to a resolution query.
DNS Caching: The local storage of DNS query results so that future requests for the same domain can be resolved without repeating the full lookup process.
Time to Live: A value in a packet that limits its lifespan on a network, preventing it from circulating indefinitely.
Caching Server: A server that stores copies of DNS query results to serve repeated requests from multiple clients without forwarding each query to authoritative DNS servers.
Hosts File: A local file on a computer that maps hostnames to IP addresses and is checked before any DNS query is made.
Fully Qualified Domain Name: The complete domain name for a host, including the hostname, all subdomains, and the top-level domain.
A Record: A DNS record type that maps a hostname to an IPv4 address.
NS Record: A DNS record type that identifies the authoritative name servers for a domain.
IP Address: A numerical label assigned to each device connected to a network that uses the Internet Protocol.

Topics

Interactive Predict

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