How many steps are there in a DNS lookup when no information is cached?

• A. 8 steps
• B. 6 steps
• C. 4 steps
• D. 10 steps

Answer: (A)

When there is no cached information, a DNS lookup must perform a full chain of lookups through the hierarchy to resolve the domain. The client sends a query to its resolver, and since nothing is cached, the resolver reaches out to a root server. The root responds with a referral to the appropriate top-level domain (TLD) server. The resolver then queries that TLD server, which replies with a referral to the domain’s authoritative nameserver. The resolver queries the authoritative server, which returns the actual IP address. The resolver caches the answer and returns it to the client. If you count every message exchange, there are eight steps: client to resolver, resolver to root, root to resolver, resolver to TLD, TLD to resolver, resolver to authoritative, authoritative to resolver, and resolver to client.