Domain Name System

IP addresses are not human readable, and they point to single machines when applications have many.

Domain name System

Distributed database of mapping between hostnames and IP addresses. Application layer protocol that runs on top of UDP.

Resource Records (name, value, type, ttl)

Type A: name - hostname, value - ip
Type NS: name - domain, value - hostname of authoritative name server for this domain

In recursive lookups, 13 root servers (IP addresses stable) that are replicated.

Any Cast: advertise a single IP prefix with multiple distinct locations. Hosts routed to closest one.

identification: reply will match query
flags: tell if query or reply
questions: query of hostname lookup
answers: responses to query
authority: if responder does not know answer, nameserver authoritative for part of the hostname
additional: to help prevent further lookups (hints for common lookups)