DNS

History

• Hosts file
  • flat namespace
  • possible duplicates
  • unwieldy

DNS What is it?

• ICANN - Internet Corporation for Assigned Names and Numbers
• IANA - Internet Assigned Numbers Authority
  • department of ICANN?
  • manages the root zone (top of hierarchy)
  • manages global pool of IP addresses

DNS What is it?

• Do we need it to use the internet?
• Registrar

• puts your domain into the global registry
• Each TLD has only one authoritative registry
  • Verisign
  • Tld registry db

The Hierarchy

A simple view

More

• OSI model? Ports? UDP
• Zone transfers always done with TCP
• UDP is almost always use to query first, but may switch to TCP if response is too large.

DNS Client View

• Youtube video
• Timeouts
• Search Domain

DNS Client View

Lookup Server View

Lookup Server Steps

• 1. Client makes request to lookup server
• 2. Lookup server checks to see if request is saved in cache
• 3. If it is, is it still valid?
• 4. Query root server to find address of tld nameserver
• 5. Query TLD server to find address of domain nameserver
• 6. Query authoritative domain server to find address of host
• 7. Store results in cache
• 8. Return results to client

Lookup server Misc

• TTL
  • Amt of time (in seconds) the record can be cached by any resolver
  • low value: more load on DNS server
  • too hi: stale cache entries
• Recursive lookups
• Security?

Authoritative Server View

Subdomains and Delegation

• When the authoritative name server for a domain receives a request for a subdomain's records and responds with NS records for other name servers, that is DNS delegation.

• visual

Master/Slave Authoritative Server Views

Finally

• Notify
• Serial Numbers