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Zorluk: OrtaTroubleshooting DNS and Name Resolution Services

A desktop technician is troubleshooting a client system that cannot connect to an internal web application hosted at `payroll.internal`. The application server was recently migrated to a new IP address (10.0.5.9010.0.5.90), and the authoritative DNS zone was updated accordingly. However, when attempting to open the application on the client workstation, network traffic is still sent to the decommissioned IP address (10.0.5.1210.0.5.12). The technician executes `ipconfig /displaydns` on the client system and receives the following command output snippet:

Record Name . . . . . : payroll.internal
Record Type . . . . . : 1
Time To Live . . . . . : 86400
Data Length . . . . . : 4
Section . . . . . . . : Answer
A (Host) Record . . . : 10.0.5.12

Which of the following identifies the root cause of this failure and the correct remediation action to take on the client workstation?

  1. The client workstation is retaining a stale mapping in its local DNS resolver cache due to a high Time To Live value; running `ipconfig /flushdns` will clear the outdated entry.Cevap
  2. B
    The client resolver is failing because Record Type 1 is invalid for IPv4 hostname resolution; the server administrator must change the zone entry to an AAAA record.
  3. C
    The client system is unable to update its local cache because TCP port 53 is blocked by the host firewall; an inbound firewall exception must be created.
  4. D
    The `ipconfig /displaydns` command output indicates a server-side lookup failure; restarting the DNS Server service on the domain controller is required to refresh the subnet.

Cevap

The client workstation holds an outdated mapping in its local DNS cache owing to a high Time To Live setting; executing `ipconfig /flushdns` on the client resolves the issue.
The correct answer correctly identifies that `ipconfig /displaydns` displays entries currently held in the client system's local resolver cache. Because the TTL (Time To Live) was configured for 86,400 seconds (24 hours), the client operating system reuses the cached IP address (10.0.5.1210.0.5.12) instead of querying the DNS server for the newly updated record (10.0.5.9010.0.5.90). Running `ipconfig /flushdns` clears this local cache and forces a new DNS lookup.

Adım Adım Çözüm

1
Analyze the command output from `ipconfig /displaydns`.
The local DNS cache contains an A record (Record Type 1) mapping `payroll.internal` to 10.0.5.1210.0.5.12 with 86,40086,400 seconds remaining on its TTL.
When a host queries a domain name, the operating system checks its local resolver cache before querying external DNS servers. A cached entry prevents new network requests from hitting the server.
2
Compare the cached entry to the actual updated infrastructure state.
The server was updated on the DNS server to 10.0.5.9010.0.5.90, but the client is still using the cached 10.0.5.1210.0.5.12 address.
Because the TTL was set high (86,40086,400 seconds or 24 hours), the client will not automatically query DNS until the cache entry expires.
3
Determine the appropriate command to invalidate the local cache.
Executing `ipconfig /flushdns` purges all entries in the Windows DNS resolver cache.
Flushing the cache forces the next application lookup to send a fresh request to the network's DNS server, obtaining the new IP address.

Anahtar Kavram

Local DNS Resolver Cache and TTL Behavior
Tahmini Süre:1m 30s
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