Purpose of DNS (problem definition)

• names for humans, numbers for computers - ancient history, the /etc/hosts file
• distributed control (ownership)
• distributed service (redundancy, availability)

DNS Client behaviour

• lookup mechanisms and behaviour
• overriding DNS with local names (use /etc/hosts)

Total system picture

• authoritative servers
• resolvers (caching, forwarding)
• domain registration and DNS

Record types

• A and AAAA, IPv4 and IPv6 addresses for known names
• PTR records, getting the name(s) for a given IP
• MX, mail eXchangers (where to send mail messages)
• NS and SOA, plumbing records
• TXT and SRV, rare records
• CNAME records (aliases)

Command line tools

• nslookup (one of the oldest)
• host (common, simple)
• dnsq (and the other djbdns-tools)

Servers

• BIND (a very common DNS server)
• djbdns (tinydns and dnscache)
• maradns
• pdns

Odds and ends

• DNS sequence numbers
• packet signatures (UDP and TCP)

A picture of the DNS system: