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- DNS, short for Domain Name System, is a hierarchical naming system connecting domain names to IP addresses.
- Components: DNS consists of three key parts: the namespace, name servers, and resolvers.
- Namespace: The DNS namespace is composed of domains, including root and top-level domains (TLDs) like .com, .edu, etc.
- Second Level Domains: These include names like Yahoo, Amazon, and PBS. LinkedIn is also a second-level domain.
- Subdomains: Situated under second-level domains, subdomains are versatile and can be structured deeply.
- Name Servers: Used for query distribution within DNS namespace, each containing data about specific domains.
- Resolvers: Client-side programs generating DNS queries; they initiate resolution processes.
- Resolution Process: Query begins inside DNS namespace, can start at ISP or specific DNS server. If needed, queries are forwarded until resolved.
- Referrals: Resolvers manage query referrals, processing requests even from unrelated clients.
- DNS Caching: Servers store resolved host names and IP addresses to expedite future queries.
- Time to Live (TTL): Cached data has a lifespan; entries are deleted after a set time.
- Query Types: DNS queries are classified into three types: recursive, iterative, and non-recursive.
- Recursive Query: DNS server handles entire resolution process; caches and forwards as needed.
- Iterative Query: DNS server sends query to other servers, compiles responses, and returns results.
- Non-Recursive Query: Resolver already has answer, either from cache or authoritative server.
- DNS Request Flow: Client query sent to ISP, which sends a recursive query to root server. Root server directs ISP to relevant domain server. The process continues iteratively until resolution, ensuring users access desired websites.
