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Zorluk: OrtaCommon Ports and Protocols

A network administrator is troubleshooting a zone transfer failure between an internal primary DNS server and a newly deployed secondary DNS server across a subnet boundary controlled by an Access Control List (ACL). Standard DNS resolution queries from client workstations to the primary server are functioning normally, but automated zone sync operations consistently fail. Which ACL modification should the administrator make to allow zone transfers while maintaining standard name resolution?

  1. Permit traffic on TCP port 53 between the DNS servers.Cevap
  2. B
    Permit traffic on UDP port 53 between the DNS servers.
  3. C
    Permit traffic on TCP port 5353 between the DNS servers.
  4. D
    Permit traffic on UDP port 67 between the DNS servers.

Cevap

Permit traffic on TCP port 53 between the DNS servers.
The correct option correctly identifies TCP port 53 as the protocol required for DNS zone transfers. Standard name resolution uses UDP port 53 because individual requests and responses are small. However, zone transfers replicate entire domain databases between primary and secondary servers, requiring the guaranteed delivery, connection management, and larger packet handling of TCP.

Adım Adım Çözüm

1
Identify the service and traffic behavior described in the scenario.
The scenario involves DNS services functioning for standard queries (UDP 53) but failing for database synchronization/zone transfers between servers.
DNS relies on different transport protocols depending on the operation size and reliability requirements.
2
Analyze transport layer requirements for DNS zone transfers.
Zone transfers (AXFR/IXFR) transmit complete resource record databases which exceed the standard 512-byte UDP payload limit and require stateful, reliable transmission provided by TCP.
TCP port 53 ensures packet sequencing, error detection, and acknowledgement during multi-packet database replication.
3
Select the option that allows the appropriate transport protocol and port combination.
Allowing TCP port 53 explicitly addresses the missing transport rule required for server-to-server replication.
Standard client queries already work over UDP 53, confirming that UDP 53 is open while TCP 53 was blocked.

Anahtar Kavram

DNS Transport Layer Dual Behavior (UDP vs TCP Port 53)
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Konular

Common Ports and Protocols

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