Domain Name System and Name Resolution Questions

Comprehensive understanding of the Domain Name System and the end to end name resolution process. Candidates should be able to explain the full query flow from a client stub resolver to a recursive resolver and onward to root name servers, top level domain name servers, and authoritative name servers, and to distinguish recursive and iterative queries and the roles of stub, recursive, and authoritative resolvers. Expected knowledge includes common resource record types and their purposes such as A and AAAA address records, CNAME alias records, MX mail exchange records, NS delegation records, SOA start of authority records and zone serials, TXT arbitrary text and verification records, PTR reverse mapping records, and SRV service records. Candidates should understand caching behavior, the role of time to live values and negative caching, how propagation delays occur, and how time to live choices affect rollouts and rollbacks. The topic covers operational impacts and common failures including misdelegation and missing glue records, stale caches and slow resolution, DNS cache poisoning and denial of service amplification, and mitigations such as domain name system security extensions, rate limiting, and validating authoritative responses. Candidates should be able to perform diagnostics using tools and commands such as dig, nslookup, host, tcpdump, and traceroute, and to run checks like querying authoritative servers, performing a trace of the resolution path, inspecting SOA serial numbers, and testing from multiple resolvers. Practical troubleshooting steps and best practices are expected, including zone verification, checking delegation chains, understanding resolver configuration and forwarders, and planning DNS changes to minimize user impact.