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Question

Difficulty: EasyDNS Infrastructure and Record Types

A network administrator is configuring a secondary DNS server to perform a full zone transfer (AXFR) from the primary name server. Which transport layer protocol and port number are used by default to execute this zone transfer?

  1. TCP port 53Answer
  2. B
    UDP port 53
  3. C
    TCP port 67
  4. D
    UDP port 69

Answer

DNS zone transfers (AXFR/IXFR) use TCP port 53 to guarantee reliable delivery of full or incremental zone database files.
DNS zone transfers (such as AXFR or IXFR) move potentially large amounts of DNS database records between name servers. To guarantee that all resource records arrive intact and in order without data loss, DNS uses TCP port 53 for zone transfers.

Step-by-Step Solution

1
Identify the type of DNS traffic being requested
The traffic is a zone transfer (AXFR) between a primary and secondary DNS server.
Standard DNS resolution queries use connectionless UDP, but bulk database transfers require reliable session delivery.
2
Determine the transport protocol and port for DNS zone transfers
Zone transfers require TCP on port 53.
TCP ensures packet sequencing, error checking, and reliable retransmission when transferring entire zone records, while port 53 is the dedicated port for DNS services.

Key Concept

DNS Transport Protocols (UDP 53 for Queries vs TCP 53 for Zone Transfers)
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Topics

DNS Infrastructure and Record Types

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