A system, managed in a distributed way by servers around the world, that maps domain names such as www.example.com to the IP addresses used for communication.
Japanese name: DNS
DNS (Domain Name System) appears in 9 practice questions across 2 topics, including Computer Networking Basics, Cloud and Container Basics.
Field: Computer Networking Basics
A device sends its query to a full-service resolver (caching DNS server) run by its ISP or organization. If the answer is not cached, the resolver asks a root server, then a TLD server such as the one for .com, then the domain's authoritative DNS server, and returns the answer to the device. Each server only says "ask this server next," so no server needs to hold all the data.
A resolver caches each answer for the validity period attached to the record (its TTL) and answers repeated queries immediately. This cuts the number of queries and the waiting time, but after a DNS setting changes, the old value may still be used until cached answers expire. That is why the TTL is lowered before moving a server.
Record types include A for IPv4 addresses, AAAA for IPv6 addresses, CNAME for aliases, MX for mail delivery and NS for a domain's authoritative DNS servers. Queries mainly use UDP port 53, and TCP is also used, for example when responses are large. Against eavesdropping and forged responses, DNSSEC signatures and encryption such as DNS over HTTPS (DoH) are used.
Answer: B. About 300 ms
First, the TCP three-way handshake takes one round trip (the client can send its first TLS message together with the final ACK). Next, the TLS 1.3 handshake takes one round trip, and then the HTTP request and response take one more, for three round trips in total: 3 × 100 = 300 ms. With TLS 1.2 the key exchange takes two round trips, giving four round trips, or 400 ms. This waiting time depends on the number of RTTs, which is set by distance, so adding link bandwidth does not shorten it. QUIC, used by HTTP/3, combines the transport and cryptographic handshakes into one round trip and also offers a way to send data in the first flight when reconnecting (0-RTT).
Answer: B. It translates domain names such as www.example.com into the IP addresses used for communication (name resolution)
DNS (Domain Name System) is the system that maps human-friendly domain names to the IP addresses used for communication. When you open a URL in a browser, the device first asks DNS for the server's IP address and then connects to that address. DNS data is not held on one server; it is divided by levels of the domain name hierarchy and managed in a distributed way by servers around the world. Queries mainly use UDP port 53, and TCP is also used, for example when responses are large.
Port 53 by default. Ordinary queries mainly use UDP, and TCP is also used for large responses or for zone transfers between servers.
Resolvers and devices cache the previous answer for the record's TTL. Until the cache expires and they query again, the old address may still be used.
DNS (Domain Name System) is the system that maps human-friendly domain names to the IP addresses used for communication.
What is the main role of DNS (Domain Name System)?It first asks a root server, which refers it to the server managing .com (a TLD server); that server refers it to the authoritative DNS server for example.com, which finally returns the address of www.example.com.
A full-service resolver (caching DNS server) with an empty …HTTP and DNS are application-layer protocols.
In the four-layer TCP/IP model, which layer do TCP and UDP …Finding an IP address from a domain name is the job of DNS, and assigning IP addresses automatically is the job of DHCP.
Which correctly describes the role of ARP?With no connection setup, no delivery confirmation and no retransmission, it is used for voice calls and live video, where a little loss is better than delay, and for DNS, which needs just one query and one response.
Which correctly describes UDP?As an Amazon Associate I earn from qualifying purchases.
HTTP (Hypertext Transfer Protocol) DHCP TLS Three-way handshake OSI reference model ARP MAC address Port number SSH Subnet mask