ماڈیول اسباق (2/3)
UDP, TCP ed EDNS(0)
UDP, TCP, and EDNS(0)
Traditional DNS commonly uses UDP for small queries. If a response does not fit the available message size, it may be marked truncated; the client can retry over TCP. TCP is a normal part of DNS, not a failure mode. Zone transfers also use TCP.
EDNS(0) extends DNS so clients and servers can signal options, including a larger UDP payload size. A larger message can reduce truncation, but oversized UDP responses may fragment and be dropped by networks. Operators should test realistic paths and avoid assuming that the largest advertised size always works.
When a query times out, distinguish packet loss, filtering, fragmentation, server load, and an actual DNS error. A timeout is not an RCODE.
Check your understanding
Choose the best answer. This quiz runs locally and sends no DNS queries to real domains.
What should a client commonly do after a truncated UDP response?