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Module 5: Application Layer & Security

20267m

Explain the hierarchical architecture of the Domain Name Space. Describe the domain name resolution process using recursive and iterative queries with a suitable sequence diagram.

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Domain Name Space

DNS is a distributed, hierarchical database mapping names to IP addresses. The name space is an inverted tree with up to 128 levels; each node has a label (max 63 characters), and a domain name is the sequence of labels from the node up to the root, separated by dots.

SVGVector Architecture Diagram (SVG)
. com edu org example mit www Root Top-level domain Second-level Host
  • Root servers know the TLD servers.
  • TLD servers (.com, .org, country codes) know authoritative servers of domains.
  • Authoritative servers hold the actual records for a zone.
  • Local/recursive resolver (from ISP) queries on behalf of clients and caches answers.

Name Resolution

Recursive query

The client asks its local resolver, which takes full responsibility for returning the final answer (or an error).

Iterative query

The queried server returns either the answer or a referral to another server; the requester contacts the next server itself.

SVGVector Architecture Diagram (SVG)
Client Local DNS Root TLD (.com) Authoritative 1 query 2 query 3 refer: TLD 4 query 5 refer: auth. NS 6 query 7 IP address 8 IP address Client to Local DNS: recursive. Local DNS to servers: iterative.

Client -> local resolver is recursive; local resolver -> root/TLD/authoritative uses iterative queries. Results are cached according to their TTL to reduce traffic.

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