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Zorluk: ZorUtilizing Command-Line Network Troubleshooting Utilities

A system administrator is troubleshooting a hostname resolution issue on a Linux workstation. Users report they cannot connect to an internal intranet site at `app.dev.local`. The administrator executes a diagnostic DNS query using `dig` and receives the following terminal output snippet:

;; QUESTION SECTION:
;app.dev.local. IN A

;; ANSWER SECTION:
app.dev.local. 300 IN CNAME web-server-01.dev.local.

;; AUTHORITY SECTION:
dev.local. 3600 IN NS ns1.dev.local.

The output shows an alias (CNAME) pointing to `web-server-01.dev.local`, but no corresponding IPv4 address (`A` record) is included in the response. Based on this command-line output, which command should the administrator run NEXT to directly query the designated authoritative server `ns1.dev.local` specifically for the missing `A` record of target host `web-server-01.dev.local`?

  1. dig @ns1.dev.local web-server-01.dev.local ACevap
  2. B
    nslookup -type=CNAME web-server-01.dev.local ns1.dev.local
  3. C
    dig +authoritative app.dev.local web-server-01.dev.local
  4. D
    netstat -a @ns1.dev.local web-server-01.dev.local:53

Cevap

Execute the command `dig @ns1.dev.local web-server-01.dev.local A` to query the authoritative name server directly for the missing A record.
The command `dig @ns1.dev.local web-server-01.dev.local A` is correct because using the `@` symbol instructs `dig` to bypass local DNS resolution and query `ns1.dev.local` directly. Specifying `web-server-01.dev.local` and `A` requests the IPv4 address mapped to the canonical hostname discovered in the CNAME response.

Adım Adım Çözüm

1
Analyze the initial `dig` output
The query for `app.dev.local` returns a CNAME pointing to `web-server-01.dev.local` and identifies `ns1.dev.local` in the AUTHORITY SECTION as the domain's primary name server.
The local recursive resolver did not append the target A record for the canonical name `web-server-01.dev.local` in the initial response.
2
Identify the required command-line syntax for querying specific DNS servers with `dig`
The `@` symbol is used in `dig` to designate a specific DNS server to query, followed by the domain name and record type.
Bypassing the local cache/stub resolver and querying `ns1.dev.local` directly confirms whether the authoritative server holds the valid A record.
3
Formulate the exact command
`dig @ns1.dev.local web-server-01.dev.local A`
This correctly targets `@ns1.dev.local` for the hostname `web-server-01.dev.local` requesting record type `A`.

Anahtar Kavram

Utilizing `dig` to perform directed DNS queries against specific authoritative name servers for specific record types.
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Utilizing Command-Line Network Troubleshooting Utilities

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