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Zorluk: ZorTroubleshooting DNS and Name Resolution Services

A systems engineer is troubleshooting a name resolution failure for an internal application alias, `app.corp.net`. When querying the primary DNS server directly using `nslookup`, the following output is returned:

text
$ nslookup app.corp.net 10.150.1.10
Server: dns01.corp.net
Address: 10.150.1.10

** server can't find app.corp.net: NXDOMAIN

Upon reviewing the primary zone configuration, the administrator confirms that `app.corp.net` exists as a valid CNAME record mapping to `web-prod-01.internal.net`. However, `web-prod-01.internal.net` is hosted in a separate private zone that is not configured on or reachable by `dns01.corp.net`.

Which of the following best explains why the DNS server returns an NXDOMAIN error for the CNAME query?

  1. The DNS server is unable to resolve the canonical host specified in the CNAME record to a valid address record within its available zones.Cevap
  2. B
    The CNAME record was improperly defined using an IP address rather than a fully qualified domain name.
  3. C
    The nslookup utility bypassed local DNS server processing and displayed a stale negative entry from the workstation's local resolver cache.
  4. D
    The CNAME alias response exceeded the 512-byte limit for UDP traffic, causing the query to fail due to TCP port 53 blocking.

Cevap

The DNS server is unable to resolve the canonical host specified in the CNAME record to a valid address record within its available zones.
When a DNS client queries a record that is configured as a CNAME (Canonical Name), the DNS server must follow the alias to the target FQDN and resolve its corresponding address (A/AAAA) record. If the target FQDN belongs to a zone that is missing, unreachable, or un-delegated, the server cannot fulfill the query chain and returns an NXDOMAIN error.

Adım Adım Çözüm

1
Analyze the command output and error code.
The command targets DNS server `10.150.1.10` directly and returns `NXDOMAIN` for `app.corp.net`.
`NXDOMAIN` (Non-Existent Domain) indicates that the server queried believes the domain name does not exist in DNS.
2
Evaluate the DNS record configuration described in the scenario.
`app.corp.net` is a CNAME record pointing to `web-prod-01.internal.net`.
Resolving a CNAME record requires a two-step resolution process: looking up the alias, and then resolving the canonical target hostname to an IP address (A or AAAA record).
3
Correlate the missing target zone with the resolution failure.
Because `web-prod-01.internal.net` resides in an unlinked private zone, the DNS server fails to complete the canonical name lookup.
If the canonical target name cannot be resolved to an IP address by the server, the final response returned to the client for the CNAME lookup is `NXDOMAIN`.

Anahtar Kavram

DNS CNAME Resolution Chaining and NXDOMAIN Failure Modes
Tahmini Süre:2m 0s
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Troubleshooting DNS and Name Resolution Services

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