DNS(Domain name system)

Domain name system

A Domain Name System (DNS) translates a domain name such as www.example.com to an IP address.

DNS is hierarchical, with a few authoritative servers at the top level. Your router or ISP provides information about which DNS server(s) to contact when doing a lookup. Lower level DNS servers cache mappings, which could become stale due to DNS propagation delays. DNS results can also be cached by your browser or OS for a certain period of time, determined by the time to live (TTL).

• NS record (name server) - Specifies the DNS servers for your domain/subdomain.

• MX record (mail exchange) - Specifies the mail servers for accepting messages.

• A record (address) - Points a name to an IP address.

• CNAME (canonical) - Points a name to another name or CNAME (example.com to www.example.com) or to an A record.

Services such as CloudFlare and Route 53 provide managed DNS services. Some DNS services can route traffic through various methods:

• Weighted round robin

  • Prevent traffic from going to servers under maintenance

  • Balance between varying cluster sizes

  • A/B testing

• Latency-based

• Geolocation-based

Disadvantage(s): DNS

• Accessing a DNS server introduces a slight delay, although mitigated by caching described above.

• DNS server management could be complex and is generally managed by governments, ISPs, and large companies.

• DNS services have recently come under DDoS attack, preventing users from accessing websites such as Twitter without knowing Twitter's IP address(es).

Source(s) and further reading

• DNS architecture

• Wikipedia

• DNS articles