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).
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NS record (name server) - Specifies the DNS servers for your domain/subdomain.
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MX record (mail exchange) - Specifies the mail servers for accepting messages.
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A record (address) - Points a name to an IP address.
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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:
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Weighted round robin
- Prevent traffic from going to servers under maintenance
- Balance between varying cluster sizes
- A/B testing
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Latency-based
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Geolocation-based
DNS disadvantages
- 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).