What is the difference between a full zone transfer (AXFR) and an incremental zone transfer (IXFR) in DNS?

• A. IXFR transfers the entire zone; AXFR transfers changes
• B. Full zone transfer
• C. Reverse lookup
• D. Dynamic update

Answer: (B)

In DNS, a zone transfer copies data from a master to its slaves, and the difference between a full and an incremental transfer is about how much data is sent. A full zone transfer (AXFR) copies every record in the zone, giving the secondary a complete, exact copy each time. An incremental zone transfer (IXFR) sends only the changes since the last transfer, using the zone’s serial number to identify updates, which saves bandwidth and speeds up synchronization for large zones with small updates. IXFR is more efficient when supported, but requires that both sides track versions correctly; if IXFR isn’t available or the secondary is far behind, a full transfer may be used to re-sync.