DNS

Domain Name System

• Convert human readable name to IP address
  • like a phone book
  • two way handshake
• Provided by service like CloudFare
• IP address usually caching on the computer
• firewall will block request if indicated
• TLD, Top Level Domain (.com)

Disadvantages of DNS

• Access to DNS server may introduce a slight delay, but can be cached locally
• Complex to manage, and usually managed by governments, ISPs and companies

1. CDN resolver - initiate query sequence and forward to other DNS name servers
2. Root-level name servers - Maintain name of server based on TLD
3. Top-level domain (TLD) name servers: These servers hold the IP addresses of authoritative name servers. The querying party will get a list of IP addresses that belong to the authoritative servers of the organisation.
4. Authoritative name servers: These are the organization’s DNS name servers that provide the IP addresses of the web or application servers.

Caching

• implemented in the browser to store DNS
  

DNS as distributed system

• avoid being single point of failure
• low query latency
• highly available across the globe
• highly reliable
  • caching
  • server replication
  • UDP protocol